THE  ANALYSIS  OF  PAINTS 

AND 

PAINTING  MATERIALS 


Published   by  the 

McGreiw-  Hill    Book.  Company 


\oi*lt 

to  theBookDepartments  of  tKe 

McGraw  Publishing  Company  Hill  Publishing"  Company 

Publishers  of  Books  for 

Electrical  World  The  Engineering  and  Mining  Journal 

Engineering  Record  Power  and  The  Engineer 

Electric  Railway  Journal  American    Machinist 

Metallurgical  and  CKemical  Engineering 


THE  ANALYSIS  OF  PAINTS 


AND 


PAINTING  MATERIALS 


BY 

HENRY  A.  GARDNER 

DIRECTOR,   SCIENTIFIC   SECTION,   EDUCATIONAL   BUREAU,   PAINT  MANUFACTURERS' 
ASSOCIATION   OF  THE  UNITED  STATES 


AND 


JOHN  A.  SCHAEFFER 

INSTRUCTOR  IN  CHEMICAL  PRACTICE,   CARNEGIE   TECHNICAL 
SCHOOLS,   PITTSBURG,   PA. 


McGRAW-HILL   BOOK   COMPANY 

239  WEST  39TH  STRFET,  NEW  YORK 

6  BOUVERIE  STREET,  LONDON,  E.  C. 

1911 


COPYRIGHT,  1910 

BY  THE 
MCGRAW-HILL  BOOK  COMPANY 


Printed  by 

The  Maple  Press 

York,  Pa. 


To 

DR.  EDGAR  F.  SMITH 
Provost-elect,    University    of    Pennsylvania, 
whose  teachings  have  been  a  source  of  in- 
spiration in  our  work,  this  book  is  dedicated. 


222495 


PREFACE. 


The  authors  are  presenting  in  this  book  a  series  of  selected 
methods  for  the  analysis  of  materials  used  in  the  manufacture 
of  paints. 

Acknowledgment  is  made  to  Walker,  Mcllhiney,  and  others 
for  several  methods  of  importance,  which  have  been  included  and 
correlated  with  new  and  valuable  methods  worked  out  by  the 
authors. 

It  is  assumed  that  the  reader  is  well  versed  in  the  ordinary 
quantitative  methods  used  in  analytical  chemistry,  and  no 
attempt,  therefore,  has  been  made  to  explain  such  methods  in 
detail. 

It  is  the  hope  of  the  authors  that  this  book  will  prove  of 
value  to  all  those  engaged  in  the  manufacture  or  use  of  painting 
materials. 
December,  1910. 


Vll 


CONTENTS. 


PAGES 

CHAPTER  I. 
The  Analysis  of  Dry  Pigments 1-39 

CHAPTER  II. 
The  Analysis  of  Mixed  Pigments  and  Paints 4O~47 

CHAPTER  III. 
The  Analysis  of  Paint  Vehicles  and  Varnishes 48-77 

APPENDIX  A. 
Analysis  of  Bituminous  Paints 78-88 

APPENDIX  B. 
Paint  Specifications 88-96 


IX 


THE  ANALYSIS  OF  PAINTS 

AND 

PAINTING  MATERIALS 


CHAPTER  I. 
THE  ANALYSIS  OF  DRY  PIGMENTS.  ! 

ZINC  OXIDE. 

Zinc  Oxide. — Zinc  oxide  contains  approximately  80  per  cent, 
of  metallic  zinc,  the  balance  being  combined  oxygen.  This 
pigment  is  completely  soluble  in  acetic  acid.  Some  varieties, 
however,  contain  a  small  percentage  of  impurities,  such  as 
lead  sulphate,  zinc  sulphate,  sulphur  dioxide,  silica,  iron,  and 
traces  of  metallic  zinc.  This  pigment  may  be  analyzed  either 
gravimetrically  or  volumetrically. 

Weigh  i  gram  into  a  beaker,  dissolve  in  acetic  acid,  filter 
off  any  insoluble  residue  and  determine  the  percentage  of  zinc 
in  the  filtrate  by  one  of  the  following  methods: 

1.  Gravimetric    Method. — Heat    the    acetic    acid    filtrate    to 
boiling.     Completely  precipitate  the  zinc  with  hydrogen  sulphide, 
and  boil  for  ten  minutes,  having  the  solution  fit  the  end  of  the 
operation  smelling  strongly  of  hydrogen  sulphide.     Filter,  wash, 
and  dissolve  the  precipitate  in  hydrochloric  acid.     Cool,   add 
sodium   carbonate   solution   drop   by   drop   until   the   solution 
becomes  turbid.  •  Heat  to  boiling,  add  2  drops  of  phenolphthalein 
solution  and  continue  the  addition  of  sodium  carbonate  solution 
until  just  alkaline,  when  the  zinc  will  be  completely  precipitated 
as  carbonate.     Filter  in  a  Gooch  crucible,  while  still  hot  wash, 
ignite  and  weigh  as  zinc  oxide. 

2.  Volumetric  Method. — Treat  the  acetic  acid  filtrate  with 
ammonium  hydroxide  until  alkaline.    Then  add  hydrochloric  acid 
until  faintly  acid.     Three  c.c.  of  concentrated  hydrochloric  acid  in 
excess  are  then  added,   the  solution  diluted  to  250  c.c.,  and 


2  ANALYSIS    OF    PAINTS  AND    PAINTING    MATERIALS. 

titrated  with  standard  potassium  ferrocyanide  as  in  the  standard- 
ization of  the  solution.  This  method  is  not  applicable  in  the 
presence  of  iron  or  manganese. 

Standardization  of  the  Ferrocyanide  Solution. — Ten  grams 
of  pure  metallic  zinc  are  carefully  weighed  off  and  dissolved  in 
hydrochloric  acid.  The  solution  is  made  up  to  i  liter  and  a 
volume  equivalent  to  .  2  gram  is  measured  out.  The  remaining 
solution  may  be  kept  for  restandardizing  the  ferrocyanide  solu- 
tion which,  on  standing,  appears  to  change  from  time  to  time.  In 
place  of  using  the  standard  zinc  solution,  .  2  gram  of  pure  metallic 
zinc  may  be  used  for  each  standardization. 

The  ferrocyanide  solution  is  made  by  dissolving  22  grams 
of  crystallized  potassium  ferrocyanide  in  a  liter  of  water.  One 
c.c.  of  this  solution  will  be  equal  to  about  .005  gram  of  metallic 
zinc. 

The  indicator  is  prepared  by  dissolving  uranium  acetate  or 
uranium  nitrate  in  water  until  a  faint  yellow  color  is  produced. 
A  5  per  cent,  solution  will  usually  give  a  good  end  reaction.  A 
number  of  drops  of  this  solution  are  placed  on  a  spot  plate,  and 
the  end  point  determined  by  introducing  a  few  drops  of  the 
solution  which  is  being  titrated. 

The  acid  solution  containing  .  2  gram  of  zinc  is  made  faintly 
alkaline  with  ammonium  hydroxide,  using  litmus  paper  to  deter- 
mine the  end  point.  Reacidify  faintly  with  hydrochloric  acid 
and  add  3  c.c.  of  concentrated  hydrochloric  acid  in  excess. 
Dilute  to  about  250  c.c.  and  heat  to  about  80°  C. 

The  hot  zinc  solution  is  divided  into  two  equal  portions. 
One  portion  is  titrated  by  slowly  running  in  a  few  c.c.  of  ferro- 
cyanide solution  at  a  time,  with  vigorous  stirring,  until  a  few  drops 
of  the  solution  give  a  brownish  tinge  to  the  uranium  acetate 
indicator  on  the  spot  plate.  The  remainder  of  the  zinc  solution, 
with  the  exception  of  a  few  c.c.,  is  now  added  to  the  titrated 
solution  and  the  end  point  again  determined.  The  titrated  solu- 
tion is  now  poured  back  into  the  original  beaker  containing  the 
few  remaining  c.c.  of  untitrated  solution.  The  titration  is 
finished  by  adding  two  drops  of  the  ferrocyanide  solution  at  a 
time,  testing  for  the  end  point  after  each  addition.  As  the  end 
point  develops  slowly,  it  is  well  to  examine  each  spot,  after 
standing  for  a  brief  time.  The  first  one  developing  a  brown  tinge 
is  taken  as  the  end  point. 


THE   ANALYSIS    OF    DRY    PIGMENTS.  3 

A  blue  color  will  appear  in  the  hot  zinc  solution  upon  the 
addition  of  the  ferrocyanide  solution.  This  color  gradually 
becomes  lighter,  and  when  the  end  point  is  reached  changes  to  a 
white.  By  repeated  titrations,  this  end  point  can  be  easily 
noted  and  serves  to  shorten  the  time  required  for  the  outside 
testing  with  uranium  acetate.  It,  however,  should  not  be  taken 
as  final,  as  the  uranium  acetate  gives  a  more  definite  end  point. 
The  blue  color  will  not  be  present  in  an  excess  of  ferrocyanide 
solution. 

It  is  necessary  to  make  a  correction  for  the  amount  of 
ferrocyanide  solution  required  to  develop  a  brown  color  in  the 
uranium  acetate  indicator  when  zinc  is  absent.  This  correction 
is  deducted  from  the  total  amount  of  ferrocyanide  solution  used 
and  will  usually  run  between  .  i  and  .  2  c.c. 

BASIC  CARBONATE— WHITE  LEAD. 

Basic  carbonate  white  lead  (2PbCO3Pb(OH)2)  contains  ap- 
proximately 80  per  cent,  metallic  lead  and  20  per  cent,  car- 
bonic acid  and  combined  water,  with  traces  sometimes  of  silver, 
antimony,  lead,  and  other  metals.  The  analysis  of  white  lead 
can  best  be  carried  out  by  Walker's*  method. 

(a)   Total  Lead. 

"  Weigh  i  gram  of  the  sample,  moisten  with  water,  dissolve 
in  acetic  acid,  filter,  and  wash,  ignite,  and  weigh  the  insoluble 
impurities.  To  the  filtrate  from  the  insoluble  matter  add  25  c.c. 
of  sulphuric  acid  (i :  i),  evaporate  and  heat  until  the  acetic  acid 
is  driven  off;  cool,  dilute  to  200  c.c.  with  water,  add  20  c.c.  of 
ethyl  alcohol,  allow  to  stand  for  two  hours,  filter  on  a  Gooch 
crucible,  wash  with  i  per  cent,  sulphuric  acid,  ignite,  and  weigh 
as  lead  sulphate.  Calculate  to  total  lead  (PbSO4  Xo .  68292  =Pb) , 
or  calculate  to  basic  carbonate  of  lead  (white  lead)  by  multiply- 
ing the  weight  of  lead  sulphate  by  0.85258. 

"  The  filtrate  from  the  lead  sulphate  may  be  used  to  test  for 
other  metals,  though  white  lead  is  only  ra  ely  adulterated  with 
soluble  substances;  test,  however,  for  zinc,  which  may  be  present 
as  zinc  oxide. 

*  P.  H.  Walker,  Bureau  of  Chemistry  Bulletin  No.  109,  revised, 
U.  S.  Dept.  of  Agriculture,  pp.  21  and  22. 


4  ANALYSIS    OF    PAINTS   AND    PAINTING    MATERIALS. 

"  Instead  of  determining  the  total  lead  as  sulphate  it  may  be 
determined  as  lead  chromate  by  precipitating  the  hot  acetic  acid 
solution  with  potassium  dichromate,  filtering  on  a  Gooch  crucible, 
igniting  at  a  low  temperature,  and  weighing  as  lead  chromate. 

(b)   Complete  Analysis. 

"  When  it  is  necessary  to  determine  the  exact  composition  of 
a  pure  white  lead,  heat  i  gram  of  the  pigment  in  a  porcelain  boat 
in  a  current  of  dry,  carbon-dioxide-free  air,  catching  the  water  in 
sulphuric  acid  and  calcium  chloride  and  the  carbon  dioxide  in 
soda  lime  or  potassium  hydroxide  (1.27  specific  gravity).  By 
weighing  the  residue  of  lead  monoxide  in  the  boat  all  the  factors 
for  determining  the  total  composition  are  obtained.  Figure 
the  carbon  dioxide  to  lead  carbonate  (PbCO3) ,  calculate  the  lead 
monoxide  corresponding  to  the  lead  carbonate  (PbCO3)  and  sub- 
tract from  the  total  lead  monoxide,  calculate  the  remaining  lead 
monoxide  to  lead  hydroxide  (Pb(OH)2),  calculate  the  water  cor- 
responding to  lead  hydroxide  and  subtract  from  the  total  water, 
the  remainder  being  figured  as  moisture. 

"This  method  assumes  the  absence  of  acetic  acid.  Thomp- 
son* states  that  acetic  acid  varies  from  0.05  per  cent,  in  Dutch 
process  white  lead  to  o .  7  per  cent,  in  some  precipitated  white 
leads.  It  is  then  more  accurate  to  determine  the  carbon  dioxide 
by  evolution;  this  is  especially  the  case  when  working  with  a  lead 
extracted  from  an  oil  paste,  as  the  lead  soap  and  unextracted  oil 
will  cause  a  considerable  error  by  the  ignition  method.  In 
determining  carbon  dioxide  by  the  evolution  method,  liberate 
the  carbon  dioxide  with  dilute  nitric  acid,  have  a  reflux  condenser 
next  to  the  evolution  flask  and  dry  the  carbon  dioxide  with  cal- 
cium chloride  before  absorbing  it  in  the  potassium  hydroxide 
bulbs. 

(c)  Acetic  Acid. 

"  It  is  sometimes  necessary  to  determine  acetic  acid.  The 
Navy  Department  specifications  demand  that  white  lead  shall 
not  contain  '  acetate  in  excess  of  fifteen  one-hundred ths  of  i 
per  cent,  of  glacial  acetic  acid.'  Thompson's  method*  is  as 
follows : 

*J.  Soc.  Chem.  Ind.,  1905,  24:  487. 


THE  ANALYSIS    OF    DRY   PIGMENTS.  5 

"  '  Eighteen  grams  of  the  dry  white  lead  are  placed  in  a  500  c.c. 
flask,  this  flask  being  arranged  for  connection  with  a  steam  supply 
and  also  with  an  ordinary  Liebig  condenser.  To  this  white  lead 
is  added  40  c.c.  of  syrupy  phosphoric  acid,  18  grams  of  zinc  dust, 
and  about  50  c.c.  of  water.  The  flask  containing  the  material  is 
heated  directly  and  distilled  down  to  a  small  bulk.  Then  the 
steam  is  passed  into  the  flask  until  it  becomes  about  half-full 
of  condensed  water,  when  the  steam  is  shut  off  and  the  original 
flask  heated  directly  and  distilled  down  to  the  same  small  bulk— 
this  operation  being  conducted  twice.  The  distillate  is  then 
transferred  to  a  special  flask  and  i  c.c.  of  syrupy  phosphoric  acid 
added  to  ensure  a  slightly  acid  condition.  The  flask  is  then 
heated  and  distilled  down  to  a  small  bulk — say  20  c.c.  Steam 
is  then  passed  through  the  flask  until  it  contains  about  200  c.c. 
of  condensed  water,  when  the  steam  is  shut  off  and  the  flask 
heated  directly.  These  operations  of  direct  distillation  and  steam 
distillation  are  conducted  until  10  c.c.  of  the  distillate  require  but 
a  drop  of  tenth-normal  alkali  to  produce  a  change  in  the  presence 
of  phenolphthalein.  Then  the  bulk  of  the  distillate  is  titrated 
with  tenth-normal  Sodium  hydroxide,  and  the  acetic  acid  cal- 
culated. It  will  be  found  very  convenient  in  this  titration,  which 
amounts  in  some  cases  to  600-700  c.c.  to  titrate  the  distillate 
when  it  reaches  200  c.c.,  and  so  continue  titrating  every  200  c.c. 
as  it  distils  over/ 

"  If  the  white  lead  contains  appreciable  amounts  of  chlorine 
it  is  well  to  add  some  silver  phosphate  to  the  second  distillation 
flask  and  not  carry  the  distillation  from  this  flask  too  far  at  any 
time. 

"  The  method  used  by  the  chemists  of  the  Navy  Department 
is  as  follows:  Weigh  25  grams  of  white  lead  in  an  Erlenmeyer 
flask,  add  75  c.c.  of  25  per  cent,  phosphoric  acid,  distil  with 
steam  to  a  500  c.c.  distillate,  add  to  the  distillate  some  milk 
of  barium  carbonate,  bring  to  a  boil,  filter,  keeping  the  solution 
at  the  boiling  point  (it  is  not  necessary  to  wash),  add  an  excess  of 
sulphuric  acid  to  the  filtrate  and  determine  the  barium  sulphate 
in  the  usual  manner;  subtract  53  milligrams  from  the  weight  of  the 
barium  sulphate  and  calculate  the  remainder  as  acetic  acid 
(BaSO4X  0.515  =CH3COOH).  The  object  of  this  rather  in- 
direct method  is  to  avoid  any  error  that  might  arise  from  fatty 
acids  being  carried  over  by  the  steam  distillation.  For  white 


6  ANALYSIS    OF    PAINTS   AND    PAINTING    MATERIALS. 

lead  that  has  not  been  ground  in  oil,  Thompson's  method  is  to 
be  preferred." 

Volumetric  Method. — The  following  volumetric  method  for  the 
determination  of  lead  has  been  found  by  the  authors  to  give  ex- 
cellent results  when  the  precautions  given  are  carefully  observed. 

A  .5  gram  sample  is  dissolved  in  10  c.c.  of  concentrated 
hydrochloric  acid  and  boiled  until  solution  is  effected.  Cool, 
dilute  to  40  c.c.,  neutralize  with  ammonium  hydroxide.  Add 
acetic  acid  until  distinctly  acid.  Dilute  to  200  c.c.  with  hot  water. 
Boil  and  titrate  with  ammonium  molybdate  as  given  in  the 
standardization  of  ammonium  molybdate. 

Standardization  of  Ammonium  Molybdate. — Four  and  one- 
fourth  grams  of  ammonium  molybdate  are  dissolved  to  the  liter, 
so  that  each  c.c.  is  equivalent  to  i  per  cent,  of  lead  when  .  5  gram 
sample  is  taken.  Standardize  with  .  2  gram  pure  lead  foil.  Dis- 
solve the  lead  in  nitric  acid,  evaporate  nearly  to  dryness,  add 
30  c.c.  of  water,  then  5  c.c.  sulphuric  acid  specific  gravity  i .  84, 
cool,  and  filter.  Drop  the  filter  containing  the  precipitated  lead 
sulphate  into  a  flask,  add  10  c.c.  hydrochloric  acid,  sp.  gr.  i  .19, 
boil  to  complete  disintegration,  add  15  c.c.  of  hydrochloric  acid, 
25  c.c.  of  water,  and  ammonium  hydroxide  until  alkaline.  Make 
acid  with  acetic  acid  and  dilute  to  200  c.c.  with  hot  water  and 
boil.  Titrate,  using  an  outside  indicator  of  one  part  of  tannic 
acid  in  300  parts  of  water. 

The  following  precautions  must  be  observed  in  carrying 
out  this  method.  Calcium  forms  a  molybdate  more  or  less 
insoluble,  and  when  calcium  is  present,  results  are  apt  to  be  high. 
However,  when  less  than  2  per  cent,  of  calcium  is  present  and 
a  high  percentage  of  lead,  there  appears  to  be  no  interference 
from  the  calcium.  This  method  is  only  good  for  samples  con- 
taining more  than  10  per  cent,  of  lead.  Should  a  lower  percent- 
age of  lead  be  present,  it  must  be  precipitated  as  the  sulphate 
then  redissolved  and  titrated  as  in  the  method  of  standardization. 

Carbonic  Acid. — The  carbonic-acid  content  of  white  lead 
may  be  determined  by  using  the  Scheibler  apparatus,  as  follows : 

One  gram  of  the  dry  pigment  is  placed  in  the  small  tube 
(B)  contained  in  the  flask  (F).  Dilute  hydrochloric  acid  is 
placed  in  the  flask  (F)  on  the  outside  of  the  small  tube.  Water 
is  brought  above  the  zero  mark  in  the  tube  (M),  by  forcing  water 
from  the  flask  (E)  by  means  of  the  bulb  (A).  On  opening  the 


THE   ANALYSIS    OF    DRY    PIGMENTS. 


M 


FIG.  i.— Scheibler  Apparatus. 


8  ANALYSIS   OF   PAINTS  AND   PAINTING    MATERIALS. 

stopcock  (D),  water  is  allowed  to  reach  a  level  on  the  zero  mark 
in  the  two  tubes  (M)  and  (N) .  The  flask  (F)  is  then  inverted  and 
the  acid  is  allowed  to  act  on  the  sample.  The  gas  evolved  passes 
into  the  rubber  balloon  (H)  which  causes  the  water  in  the  tube 
(M)  to  lower  and  that  in  (N)  to  rise.  The  pinchcock  (K)  is 
opened  and  the  water  is  allowed  to  flow  out  of  the  tube  (N)  at 
such  a  rate  so  that  the  liquid  in  the  two  tubes  will  be  on  the 
same  level,  as  nearly  as  possible.  When  the  gas  ceases  to  come 
off,  the  pinchcock  (K)  is  closed  and  the  apparatus  allowed 
to  stand  for  several  minutes,  after  which  the  flask  (F)  is  shaken 
several  times  so  as  to  complete  the  action.  After  action  has 
ceased,  which  should  take  place  in  from  a  half  to  three-quarters 
of  an  hour,  the  water  in  the  two  tubes  is  brought  to  the  same 
level  and  the  amount  of  gas  which  has  been  evolved  is  noted. 
It  is  essential  that  temperature  and  barometric  readings  be  made 
at  the  same  time,  so  that  corrections  may  be  made  for  errors 
arising  from  these  factors.  The  calculation  is  made  directly 
by  referring  to  the  volume  of  carbon  dioxide  evolved  at  the 
given  temperature  and  pressure  in  the  tables  which  are  given  for 
this  conversion,  making  correction  also  for  the  absorption  of 
carbon  dioxide  in  dilute  hydrochroric  acid,  the  tables  taking 
directly  into  account  the  errors  arising  from  temperature  and 
pressure.  In  some  cases  where  calcium  carbonate  is  present  in  a 
pigment  made  from  dolomitic  limestones,  it  is  necessary  that  the 
contents  of  the  flask  be  boiled,  although  this  need  be  done  only 
in  rare  cases. 

The  following  Dietrich  tables  are  so  arranged  that  the  con- 
versions can  easily  be  made. 


THE  ANALYSIS    OF    DRY    PIGMENTS. 


O 


ON  ON  co  iO          OO  <N\o  O  ""t" 

t->»  O  CS  ?O  ^  NO  t"*»  ON  O 

co  ^"  *O          NO  *>•          00  ONO 


ON          rj-          r^.          M 
O  \O  O  & 


0 

ON 


OOO 
rJ-O 


to         ^          to         t^.        oo 
10        vo          t^        co 


ON 

ON 


VH  % 

1    8s 

3    -s 


I 


\O 
a 


tOT)-iO\O 


^O 

ON 


H  10  ON  co 

ON  Tj-  10  NO  CO 

\f)  \n        \o          r-        co          ON 


MVOOO  ^-t-.0  ^°°  NVON 

•*CN      TtCO^-^-1^-lOTf-tOrl-lOTt-lOT)-lO<<d-lO<*XO 
H  <N  co^tOO  r^CO  ON 

M  CN  CO  ^~  1O  NO  t^*  CO  ON 

H  04  CO^^ONO  t^OO  ON 

H       H       M       CO     W       *^t"      W       XO     W       1O     H       l-O     W       1O     H       IO     H       1O     H       IO 
H  0)  CO^J-IONO  t^-OO  ON 

)     c«    *O     t«    *o     en 

uuouuouuuuuooucJduuuu 

U  U  O  U  U  O  U  U  U  CJ  U  CJ  CJ  U  CJ  U  U  U  U  U 


10  ANALYSIS    OF    PAINTS   AND    PAINTING    MATERIALS. 


s  .s 

iMiis  «sia  gji|i 

£££  2>¥ 

| 

CO 

gn 

<v)  oo 

t>«*     d 

88888      88888      88888 

88888 

8 

S  .£ 

IHH   g5VSE  E1U| 

l~^  vO     lO    TJ-     ro 

0 

§ 

Q 

II 

88888      88888      88888 

88888; 

8 

I 

s.s 

rf  vO      ON    w      ro            ^O  ^O    OO     O      W              co    ^O  ^O    OO      O^ 

O       H       04       CO     ^~ 
t^*  *O      lO    ^t"     <^O 

VO 

p 

'a 
o 

•3 

88888      88888      88888 

88888 

8 

3 

o 

"8 

s.s 

ifcgsi  ft^g.g  «i^ 

10  VO      t^  00      CN 
vo     10    T)-    PO    w 
vO    vO    vO    vO    vO 

vO 

BLE  II. 

entimetei 

°°, 

vO 
IS    00 

8  8  8  8  8      88888      88888 

80    o    o    o 
OOOO 

8 

<   o 

H     .0 

JQ 

3 
O 

SO 

3  £££  K      ^^^82      0^^^?.^ 

vO     vo    ^~    ro    04 

\O    vO    vO    vO    vO 

VO 
vO 

L  of  One 

Sao 
t>«   <s 

8  8  8  8  8      88888      88888 

88888 

H 

8 

O 

S.S 

g^i,i  isisE  n$H 

\o    r^  oo    o>   O 

iO    TJ-     ro     IS      N 

O    vO    vo    vO    vO 

H 

vO 

0 

CO 

M 

cs    oo 

88888      88888      88888 

88888 

8 

! 

r-.   « 

'o 

n 

s.s 

^S^     g'ggBj      Hjrij 

1-1     <N     ro    Tf    10 

VO 

N  oo 

88888      88888      88888 

88888 

8 

1 

t^  M 

* 

6 

0 

vo  vo     r-~.  00     O^ 

0 

THE   ANALYSIS    OF    DRY    PIGMENTS. 


II 


1 

d 
t-~ 

CO     C 

NO 
^t 

ON 

CM 

8 

d 

*•„ 

| 

ON 

CO     C 

Tt 

ON 

o 

0 

d 

ON 

§ 

JH 

CO     C 

CM 

* 

ON 

8 

CM 

d 

s- 

1 

<r> 

CO     C 

* 

ON 

0 

o 

CM 

d 

ON 

to 

CO     C 

0 

CO 

ON 

8 

R 

CM 

a 

g 

d 

CO 

00     C 

ON 

NO 

rO 

CO 

CM 

_ 

§ 

d 

0 

CO     C 

^ 

ON 

rj- 

CO 

5 

CM 

& 

M       O       ON   CO      l^. 

t^*    t^*  NO    NO    NO 


8O  OOOOO  OOOOO  OOOOO  O 

O  OOOOO  OOOOO  OOOOO  O 


88888   88888   8888 


OOJ^ 


8OO     OOOOO     OOOOO     OOOOO 
OO     OOOOO     OOOOO     OOOOO 


88888   88888   88888   88888   8 


88888   88888   88888   88888   8 


ON          COt^ 


12 


ANALYSIS    OF    PAINTS  AND    PAINTING    MATERIALS. 


^ 

d  .2 
£   N 

^"  ^O    OO     O     d             co    ^O  vO    OO     ON            M     c^     co    Tf*    to          VO     t1*^  OO     O\    O             H 

t^,VOlOlOTJ"                 CO^MOOs                ONOOt-^O^O                ^-COCIHH                   O 

s 

o 

\O      ON 

88888      88888      88888      88888      8 

O^ 
S 

ch  Tabl 

d     ^ 

ONMCOtot^          OOOHro^h          vOt^.OOO'O            HWco^to          vO 
vO'OtO'i-ro            <N<MHOON          OOt^-vototo            rJ-co^HO             ON 

c 

« 

"    00 
%    0\ 

88888      88888      88888      88888      8 

5 

8 

S 

g    d 

^*  vO    OO     O     W             co    ^o  \O    00     C^            w     W     co    ^*    to          vO     l^*  CO     ON    O             H 

0 

•o 

<o    £ 

88888      88888      88888      88888      8 

3 

u 

! 
S 

S   oo 

s^sjr  J^TK  pgls  m»  * 

HH 

1—  1 

•8 

«    0 
to    ON 

88888      88888      88888      88888      8 

s 

1 

a 

1 
o 

O 

6  -2 

•^•^OOOOW              fOtot^OOO              HCO^f"tovO              t^OOONOH              W 
tO^cotOW             HOONOOOO             t^.vOto^-co            OiHOOO^          OO 

ua 

3 

to    ON 

8  ?  8  8  8      88888      88888      88888      8 

0 

1 

ts 

S 

n 

S  -2 

0 

OS 

S     £ 

o     • 

to     ON 

88888      88888      88888      88888      8 

"S 
B 

& 

"o3 

S"1     »o 

ttsij  ii^i  iajgi  Et^ii  R 

u 

0) 

88888      88888      88888      88888      8 

Q 

.S 

t~^     W 

•a 
1 

K 

O      H      W      ro    ^"             to  vO     t^*  CO      O1*            O      w      w      co    ^t"             to  ^O      t^-*  00      O^            O 

THE   ANALYSIS    OF   DRY    PIGMENTS. 


ON    H     ro    ^  vO  oO     ON    H      CN     co 

H-i-i  O     O     ON  OO     r~»  vO     v/->    10    TJ-    ro  CM     H     o     ON  OO           OOt^vOvori-           co 

g    00  ONONOOOOOO  COOOOOOOOO  COCOOCt^t^            r-.t^t>»t^t^            t^ 

S  d  I  §  8  §  I  88888  88888      88888      8 

go  ON  oo   oo   co   co  ooocoooo'co  co   oo   oo    t-  r»         r^t^.t^.r^i^          t^ 

2.  o  11^88  88888  88888   88888   8 

r-  to 

2'^  ooooooooco  coooooooco  oooot^t^-t^          r^r^t^t^r^          t— 

o  2s  88888  8888888888      88888      8 

t^    co 

_<•     d  Tt-vOOOOH  ro^vOt^CO  O 

H-rt  ON  OO      r—    t^  VO  vorj-ro<NH  H 

S^-i  oooocooooo  oooooooooo  oo 

8  o  |     8  8  8  8  8  88888  88888      88888      8 

Qs     M       CO     ^-O   \O  CO       ON     W       CO     T^  IO  VO       t^»  CO       ^  O       H       CS       CO     ^"  1O 

H    ••-»  CO    OO      ****  ^      iO  Tf"     (*O    ^O    W      H  O      O^  OO      t^»  ^O             VO      *O    T^     CO     CS               H 

g^Q  OOOOOOOOOO  OOOOOOOOOO  OOt^t^t^t^             i>.t^r^t^t^             t^ 

o  5  88888  88888  88888   88888   8 

t-^    fO 

_;d'  ^VOOOOH  covovOt^ON  OHCO^VO           vovOt^OOON            O 

H    •«-!  OO     r^*  vO    vO     vo  TJ"    ro    cs     M     O  O     ON  GO     t^*  vo            vo    ^~    co    CN     M            H 

SQQ  OOOOOOOOOO  OOOOOOOOOO  COt^l>-l>.t^              t^t^t^t^t^.              t^. 

^  o  88888  88888  88888   88888   8 

t^    co 

•  j-j  ONHCOIOI^  OOOHro-* 
go  co"oo"o?oo>oo  cx°cx?oooooo 

«  o  88888  88888  88888   88888   8 

t^.    co 

•  o 

O  O      H      W      co    ^}"  ^O  \O      l>*  00      O^  O      w      CJ      CO    ^t"             ^O  \O      t"*»  00      ON            O 

(J  HHHHM  HMMHH  C^MWC^C^                 C^WC<W<N                 CO 


14  ANALYSIS    OF    PAINTS   AND    PAINTING    MATERIALS. 


FIG.  2. — Carbon  Dioxide  Apparatus. 


THE   ANALYSIS    OF    DRY    PIGMENTS.  15 

The  authors  and  de  Horvath  have  developed  the  following 
method  as  a  simple  and  more  efficacious  means  of  determining 
the  carbonic-acid  content  of  paint  pigments. 

The  method  can  be  used  in  such  cases  where  the  substances 
to  be  analyzed  evolve  gases  other  than  carbon  dioxide;  that  is, 
hydrogen  sulphide,  sulphur  dioxide,  or  organic  matter.  The 
apparatus  used  is  shown  in  the  accompanying  diagram.  A 
weighed  sample  of  the  substance  is  introduced  into  the  Erlen- 
meyer  flask  (A).  Into  flask  (B)  is  placed  a  10  per  cent,  solution 
of  barium  chloride,  more  than  sufficient  to  hold  the  carbon 
dioxide  evolved,  and  20  c.c.  of  concentrated  ammonium  hy- 
droxide free  from  carbon  dioxide.  If  sulphides  are  present,  it  is 
sometimes  advisable  to  pass  the  liberated  gas  first  through  a  few 
c.c.  of  strong  potassium  permanganate.  The  flask  (B)  is  warmed 
until  completely  filled  with  ammonia  fumes.  Flask  (D)  is  a 
safety  bottle  containing  the  same  solution  as  flask  (B).  Only 
in  rare  cases  will  any  trace  of  carbon  dioxide  be  noticed  in  the 
safety  flask.  After  flask  (B)  is  completely  filled  with  ammonia 
vapor,  make  all  connections  and  allow  the  hydrochloric  acid 
to  drop  slowly  from  the  separatory  funnel  into  the  decomposition 
flask  (A).  When  effervescence  has  ceased,  heat  the  contents 
of  the  flask  until  filled  with  steam.  The  delivery  tubes  and 
sides  of  the  precipitating  flask  are  then  washed  with  boiling 
water,  the  flask  is  filled  to  the  neck,  stoppered,  and  the  precipi- 
tated barium  carbonate  allowed  to  settle.  Wash  thoroughly  by 
decantation,  each  time  stoppering  the  flask  to  prevent  any  error 
from  the  carbon  dioxide  present  in  the  air,  and  determine 
either  gravimetrically,  by  conversion  into  barium  sulphate, 
or  volumetrically,  by  dissolving  in  standard  hydrochloric  acid 
and  titrating  the  excess  of  acid  used  with  standard  potassium 
hydroxide.  Calculate  the  barium  found  to  carbonate  and  the 
amount  of  carbon  dioxide  from  the  found  carbonate.  The 
entire  operation  may  be  hastened  by  conducting  a  brisk  current 
of  air  free  from  carbon  dioxide  through  the  entire  apparatus. 

A  few  typical  analyses  of  white  lead,  for  impurities,  are 
given. 


l6  ANALYSIS    OF   PAINTS  AND    PAINTING    MATERIALS. 


O  00  O  f*5  G  SH  M  C  O  G  r^  vo  ro  O  H  00 
ioOOHOOHOoOHOOMM\O 
OOOOGGOflOGOOOOOcs 


\o     1* 


OOCONNGGHGoGrJ-Tj-OTj-Tj-lO 
rfOOcsOOoOoOOOOOrt-iO 

oooortfiofloflooooow 

H     ir>    O     &     V     ®     rh    02    vo     D     (M     N     r^-iotoo 
lOHOOflPlofiOfHOfO 

;     ;     ;     :  !     i     '     !   j    8  I 


<3<lPQi72CJO<;NSoA<l!/5O< 


THE   ANALYSIS    OF    DRY   PIGMENTS.  17 

Metallic  lead  which  comes  to  the  corroder  may  contain  very 
minute  traces  of  metals,  such  as  silver,  copper,  bismuth,  cadmium, 
antimony,  arsenic,  iron,  nickel,  copper,  zinc,  and  manganese. 
Should  an  analysis  of  metallic  lead  be  necessary,  it  can  be  best 
carried  out  by  the  methods  outlined  by  Fresenius'  Quantitative 
Chemical  Analysis,  Vol.  II,  pp.  584  to  593.  The  method  is 
here  omitted  owing  to  the  large  number  of  references  which 
must  be  necessarily  followed  in  making  an  examination  for  the 
above  impurities. 

Basic  Sulphate— White  Lead  (Sublimed  White  Lead).— Basic 
sulphate  white  lead  shows  approximately  70  to  75  per  cent,  of 
lead  sulphate,  20  per  cent,  lead  oxide,  and  5  per  cent,  zinc  oxide. 
The  Hughes*  method  for  the  analysis  of  this  pigment  has,  by 
long  experience,  been  found  to  give  the  best  results. 

Total  Sulphates. — Mix  in  a  beaker  1/2  gram  sample  with  3 
grams  sodium  carbonate.  Add  30  c.c.  of  water  and  boil  gently 
for  ten  minutes.  Allow  to  stand  for  four  hours.  Dilute  with  hot 
water,  filter,  and  wash  until  nitrate  is  about  200  c.c.  in  vol- 
ume. Reject  the  residue.  By  this  reaction  all  the  lead  sulphate 
is  changed  to  carbonate  and  the  nitrate  contain  sodium  sulphate. 

Acidulate  the  nitrate  with  hydrochloric  acid.  Boil,  and 
add  a  slight  excess  of  barium  chloride  solution.  When  the 
precipitate  has  well  settled,  filter  on  an  ashless  filter,  wash, 
ignite,  and  weigh  as  BaSO4. 

Lead  (Method  i). — Dissolve  i  gram  of  sample  in  100  c.c. 
of  a  solution  made  as  follows: 

Eighty  per  cent,  acetic  acid,  125  c.c. 

Concentrated  ammonia,  95  c.c. 

Water,  100  c.c. 

Add  this  solution  hot  and  dilute  with  about  50  c.c.  of  water. 
Boil  until  dissolved. 

Dilute  to  200  c.c.  and  titrate  with  standard  ammonium 
molybdate  solution,  spotting  out  on  a  freshly  prepared  solution 
of  tannic  acid.  The  details  of  this  method  are  given  under  the 
analysis  of  basic  carbonate  white  lead. 

Ammonium  molybdate  is  a  slightly  variable  salt,  but  a 
solution  containing  8 . 67  grams  per  liter  usually  gives  a  standard 
solution: 

*  L.  S.  Hughes,  chief  chemist,  Picher  Lead  Co. 

2 


1 8  ANALYSIS    OF   PAINTS   AND    PAINTING    MATERIALS. 

i  c.c.  equals  .01  gram  Pb. 
Standardize  against  pure  PbO  or  pure  PbSO4. 
Lead   (Method  2). — Treat  sample  as  above  until  dissolved. 
If  solution  is  not  quite  clear,  filter.     Add  to  filtrate  an  excess 
of  potassium  bichromate  solution.     Boil  and  stand  in  a  warm 
place  until  well  settled.     Filter  on  a  Gooch  crucible,  ignite  below 
a  red  heat  and  weigh  as  PbCrO4. 
Factor  for  lead  equals  .  64. 

Zinc. — Boil  i  gram  of  sample  in  a  beaker  with  the  following 
solution: 

Water,  30  c.c. 

Ammonium  chloride,  4  gms. 

Concentrated  hydrochloric  acid,  6  c.c. 

If  sample  is  not  quite  dissolved,  the  result  is  not  affected, 
as  the  residue  is  lead  sulphate  or  precipitated  lead  chloride. 

Dilute  to  200  c.c.  with  hot  water  and  titrate  with  a  standard 
solution  of  potassium  ferrocyanide,  spotting  out  on  a  5  per  cent, 
solution  of  uranium  nitrate. 

Forty-three  grams  per  liter  of  potassium  ferrocyanide  usually 
gives  a  solution  approximately — i  c.c.  equals  .01  gram  Zn. 
Standardize  against  freshly  ignited  ZnO  or  pure  metallic  zinc. 

Sulphur  Dioxide. — Digest  2  grams  with  frequent  stirring 
in  5  per  cent,  sulphuric  acid  for  ten  minutes  in  the  cold. 

Add  starch  indicator  and  titrate  with  N/ioo  iodine  solution. 

A  more  accurate  method  is  to  add  an  excess  of  the  standard 
iodine  solution  to  the  sample  before  addition  of  the  acid  and  then 
to  titrate  the  excess  of  iodine  with  N/ioo  sodium  thiosulphate 
solution. 

Calculations. — Calculations  can  be  simplified  by  bearing 
in  mind  the  following  relations: 

Weight  of  BaSO4  X  i .  3  =  weight  PbSO4. 

Deduct  from  the  total  lead  the  lead  represented  by  the  lead 
sulphate  and  calculate  the  residual  lead  to  PbO. 

Calculate  the  Zn  found  to  ZnO. 

Report  the  sulphur  dioxide  found  directly,  as  it  does  not  exist 
as  a  sulphite,  but  is  instead  an  apparently  occluded  gas. 

Zinc  Lead  and  Leaded  Zinc. 

Zinc  lead  is  approximately  50  per  cent,  zinc  oxide  and  50 
per  cent,  lead  sulphate.  Leaded  zinc  varies  considerably  in  its 

- 


THE   ANALYSIS    OF    DRY    PIGMENTS.  19 

composition,  though  it  contains  on  an  average  25  per  cent,  lead 
sulphate  and  75  per  cent,  zinc  oxide.  Both  are  apt  to  contain 
traces  of  zinc  sulphate,  sulphur  dioxide,  arsenic,  and  antimony. 
The  analysis  of  such  compounds  is  carried  out  in  the  following 
way: 

Moisture. — Dry  2  grams  of  the  sample  at  105°  C.  for  two 
hours.  The  loss  will  be  moisture. 

Lead  and  Zinc. — Treat  one  gram  of  the  sample  in  a  beaker 
with  10  c.c.  of  water,  10  c.c.  of  concentrated  hydrochloric  acid, 
and  5  grams  of  ammonium  chloride.  Heat  on  the  steam  bath 
for  a  few  minutes,  dilute  to  about  300  c.c.,  boil,  filter,  wash,  and 
weigh  any  insoluble  residue.  In  a  pure  leaded  zinc  or  zinc  lead 
compound  no  residue  should  remain.  Examine  the  residue, 
should  any  be  present.  The  lead  is  completely  precipitated  in 
the  filtrate  with  hydrogen  sulphide  in  the  cold.  Allow  to  settle, 
filter,  wash,  dissolve  in  nitric  acid,  evaporate  in  the  presence  of 
sulphuric  acid,  and  determine  the  lead  either  volume  trie  ally 
or  gravimetrically,  as  stated  in  the  analysis  of  basic  carbonate 
white  lead.  The  filtrate  from  the  lead  sulphide  precipitate  is 
made  alkaline  with  ammonium  hydroxide,  any  precipitate  form- 
ing, due  to  the  presence  of  iron,  being  filtered  off,  redissolved  in 
hydrochloric  acid,  oxidized  with  a  little  nitric  acid,  reprecipi- 
tated  with  ammonia,  washed  and  weighed.  The  ammoniacal  fil- 
trate is  made  slightly  acid  with  acetic  acid,  heated  to  boiling,  and 
the  zinc  is  precipitated  as  zinc  sulphide,  filtered,  washed,  and  de- 
termined either  gravimetrically  or  volume trically,  as  stated  under 
the  analysis  of  zinc  oxide.  The  operation  may  be  hastened  by 
titrating  the  zinc  directly  after  the  removal  of  the  lead,  as  stated 
in  the  volumetric  determination  of  the  zinc.  The  filtrate,  after 
precipitating  the  zinc  as  sulphide,  is  examined  for  calcium  and 
magnesium  in  the  usual  way.  Should  calcium  or  magnesium  be 
present,  it  is,  of  course,  understood  that  the  zinc  must  first  be 
removed  as  sulphide  before  titration  in  order  to  determine  the 
calc'um  and  magnesium  present. 

Soluble  Sulphate. — One  gram  of  the  sample  is  boiled  with 
100  c.c.  of  a  mixture  containing  one  part  alcohol  and  three  parts 
of  water.  Filter  and  wash  with  a  similar  mixture  of  alcohol 
and  water,  and  determine  the  sulphuric  acid  in  the  filtrate  by 
precipitation  with  barium  chloride  as  barium  sulphate.  The 
sulphate  thus  found  is  calculated  to  zinc  sulphate.  Any  zinc 


2O  ANALYSIS    OF    PAINTS  AND   PAINTING    MATERIALS. 

remaining  after  the  calculation  to  zinc  sulphate  is  calculated  to 
zinc  oxide  and  reported  as  such. 

Total  Sulphate. — One  gram  of  the  sample  is  treated  with 
10  c.c.  of  water,  10  c.c.  of  strong  hydrochloric  acid,  and  5  grams 
of  ammonium  chloride,  in  a  large  beaker.  Heat  in  a  steam 
bath  for  a  few  minutes,  dilute  with  hot  water  to  about  300  c.c., 
boil,  and  filter  off  any  insoluble  residue.  Heat  the  filtrate  to 
boiling  and  determine  the  sulphate  present,  by  precipitation 
with  barium  chloride  as  barium  sulphate,  in  the  usual  way. 
Calculate  the  total  sulphate  present,  deduct  from  it  the  soluble 
sulphate,  and  calculate  the  remainder  to  lead  sulphate.  Any 
lead  remaining  after  the  calculation  to  lead  sulphate  is  calculated 
to  lead  monoxide. 

The  authors  find  the  iodine  test  for  the  determination  of  SO2 
in  zinc  lead  and  leaded  zinc,  as  shown  under  the  analysis  of 
sublimed  white  lead,  of  great  value. 

LITHOPONE. 

Lithopone  is  a  chemically  precipitated  pigment  containing 
approximately  70  per  cent,  barium  sulphate,  30  per  cent,  zinc 
sulphide,  with  occasionally  occluded  impurities,  such  as  zinc 
oxide,  barium  chloride,  and  barium  carbonate. 

The  following  method  after  repeated  trials  by  the  authors  is 
considered  best  for  the  analysis  of  this  pigment. 

Moisture. — Heat  2  grams  of  the  sample  for  two  hours  at 
105°  C.  The  loss  will  be  moisture.  This  should  be  less  than 
one-half  of  i  per  cent. 

Barium  Sulphate. — Treat  i  gram  of  the  sample  with  10  c.c. 
of  concentrated  hydrochloric  acid.  Add  5  c.c.  of  bromine  water. 
Evaporate  the  solution  to  one-half  its  volume  on  a  water-bath. 
Next  add  100  c.c.  of  water  and  a  few  drops  of  dilute  sulphuric 
acid.  Boil,  filter,  wash,  and  weigh  the  insoluble  residue  which 
should  show  only  the  presence  of  barium  sulphate.  Examine 
the  insoluble  residue  for  silica  and  aluminum.  Examine  the  resi- 
due as  before  stated. 

Total  Zinc. — Determine  the  total  zinc  in  the  filtrate,  either 
gravimetrically  or  volumetrically,  as  given  under  Zinc  Oxide  on 
page  i. 

Zinc  Sulphide. — One  gram  of  the  sample  is  digested  at  room 


THE   ANALYSIS    OF    DRY    PIGMENTS.  21 

temperature  with  100  c.c.  of  i  per  cent,  acetic  acid  for  one  hour. 
Filter  and  wash  the  insoluble  residue.  Transfer  this  residue  to  a 
beaker,  boil  with  dilute  hydrochloric  acid,  and  titrate  the  zinc 
directly,  as  given  under  Zinc  Oxide.  The  soluble  zinc  may  also 
be  determined  in  the  filtrate  by  one  of  the  methods,  as  outlined. 
Zinc  soluble  in  acetic  acid  is  reported  as  oxide;  zinc  insoluble, 
as  zinc  sulphide.  The  filtrate  from  the  acetic  acid  treatment, 
after  precipitating  the  zinc  as  zinc  sulphide  and  subsequent  re- 
moval, should  be  examined  for  barium  which  might  be  present 
as  carbonate,  and  calcium,  present  as  sulphate  or  carbonate. 
The  presence  of  barium  carbonate  is  unusual.  The  average 
amount  of  zinc  present  as  zinc  oxide  in  pure  lithopone  will 
usually  be  below  2.5  per  cent.,  though  sometimes  as  high  as 
5  per  cent. 

Soluble  Salts. — Digest  a  2 -gram  sample  with  50  c.c.  hot 
water  and  test  the  filtrate  for  soluble  impurities. 

BARYTES  AND  BLANC  FINE. 

These  pigments  are  the  natural  and  chemically  precipitated 
forms,  respectively,  of  barium  sulphate.  They  vary  in  their 
percentage  oi  barium  sulphate,  according  to  their  purity.  The 
content  of  barium  sulphate  should  not  be  less  than  95  per  cent. 
The  method  as  used  for  the  analysis  of  these  pigments  is  as 
follows : 

Moisture. — Heat  2  grams  of  the  sample  at  105°  C.  for  two 
hours.  The  loss  will  be  moisture. 

Loss  on  Ignition. — Ignite  i  gram  of  the  sample  for  one- 
half  hour.  The  loss  will  be  organic  matter,  free  and  combined 
water,  and  carbon  dioxide  from  any  carbonate  present.  This 
loss  should  be  reported  as  loss  on  ignition. 

Barium  Sulphate. — Treat  i  gram  of  the  sample  with  20  c.c. 
of  dilute  hydrochloric  acid.  Boil,  evaporate  to  dryness,  moisten 
with  hydrochoric  acid,  and  take  up  with  water.  Boil,  filter,  and 
wash.  Should  lead  be  present  in  the  insoluble  residue,  as  shown 
by  the  action  of  hydrogen  sulphide,  treat  the  insoluble  residue 
with  a  little  i :  i  hydrochloric  acid  and  several  drops  of  sulphuric 
acid.  Filter,  wash,  and  weigh  the  insoluble  residue.  Should 
lead  be  absent,  the  last  treatment  may  be  omitted.  Treat  the 
insoluble  residue  after  washing  with  an  excess  of  hydrofluoric 


22  ANALYSIS    OF   PAINTS  AND    PAINTING    MATERIALS. 

acid  and  a  few  drops  of  sulphuric  acid.  Evaporate  to  dryness, 
ignite,  and  determine  any  loss.  This  loss  will  be  silica.  Ex- 
amine the  filtrate  for  aluminum  oxide,  iron  oxide,  and  calcium 
oxide  in  the  usual  way. 

Soluble  Sulphate. — Soluble  sulphates  should  be  determined 
by  treating  i  gram  of  the  sample  with  20  c.c.  of  dilute  hydro- 
chloric acid.  Dilute  with  200  c.c.  of  hot  water,  boil,  filter,  wash, 
and  determine  the  sulphate  with  barium  chloride  in  the  usual 
way.  Calculate  to  calcium  sulphate.  If  carbonates  are  present, 
as  shown  by  effervescence  with  hydrochloric  acid,  calculate  the 
remaining  calcium  oxide  to  carbonate.  If  absent,  report  as 
calcium  oxide. 

WHITING  AND  PARIS  WHITE. 

These  pigments  are  the  natural  and  artificial  forms,  respect- 
ively, of  calcium  carbonate.  Dissolve  one  gram  in  hydrochloric 
acid,  filter,  determine  the  calcium  in  the  filtrate,  as  stated, 
under  Gypsum.  Determine  the  carbonic  acid  by  the  author's 
short  method,  as  outlined  under  the  estimation  of  CO2.  Deter- 
mine the  impurities  as  usual. 

GYPSUM. 

This  pigment  comes  to  the  paint  trade  in  either  the  hydrated 
or  burnt  variety.  The  amount  of  water  contained  in  this 
pigment  should  therefore  be  carefully  determined. 

Total  Water. — Ignite  i  gram  of  the  sample  to  constant 
weight.  The  loss  will  be  free  and  combined  water,  if  carbonates 
are  absent. 

Moisture. — Heat  2  grams  of  the  sample  at  105°  C.  for  two 
hours.  The  loss  will  be  uncombined  water. 

Calcium. — Calcium  is  determined  by  one  of  the  following 
methods : 

Gravimetric  Method. — Treat  one  gram  of  the  sample  with 
dilute  hydrochloric  acid.  Add  150  c.c.  of  water.  Boil,  filter, 
and  determine  the  insoluble.  Precipitate  the  aluminum  ox- 
ide and  iron  oxide  in  the  filtrate  with  ammonium  hydroxide 
and  determine  in  the  usual  way.  The  slightly  ammoniacal 
solution  is  heated  to  boiling.  A  boiling  solution  of  25  c.c.  satu- 
rated ammonium  oxalate  is  added  and  the  solution  allowed  to 


THE   ANALYSIS    OF    DRY    PIGMENTS.  23 

stand  from  one  to  two  hours  or  boiled  continuously  for  one-half 
hour.  Filter  off  the  precipitated  calcium  oxalate,  wash  with 
boiling  water,  and  ignite  for  fifteen  or  twenty  minutes  with  a 
Bunsen  burner  to  constant  weight.  Weigh  as  calcium  oxide 
and  calculate  to  calcium  sulphate.  Determine  the  magnesium 
in  the  filtrate  in  the  usual  way. 

Volumetric  Method. — The  method  as  outlined  by  Treadwell 
and  Hall*  is  excellent.  "The  calcium  is  precipitated  in  the  form 
of  its  oxalate,  filtered  and  washed  with  hot  water.  The  still  moist 
precipitate  is  transferred  to  a  beaker  by  means  of  a  stream  of 
water  from  the  wash-bottle,  and  the  part  remaining  on  the  filter 
is  removed  by  allowing  warm  dilute  sulphuric  acid  to  pass 
through  it  several  times.  To  the  turbid  solution  in  the  beaker, 
20  c.c.  of  sulphuric  acid  i :  i  are  added  and  after  dilution  with  hot 
water  to  a  volume  of  from  300  to  400  c.c.,  the  oxalic  acid  is 
titrated  with  N/io  potassium  permanganate  solution.  One  c.c. 
of  N/io  KMnO4  =0.0020  gm.  Ca." 

The  sulphuric-acid  content  is  determined  by  dissolving  i  gram 
of  the  sample  in  concentrated  hydrochloric  acid,  precipitating 
and  weighing  as  barium  sulphate,  in  the  usual  way. . 

Silica  Pigments:  Silex,  Asbestine  and  China  Clay. — The  use 
of  the  microscope  in  making  a  rough  examination  of  these 
pigments  is  very  valuable,  as  they  all  show  different  characteris- 
tics, the  asbestine  being  long  and  rod-like  in  its  particle  shape, 
the  china  clay  tabloid  in  shape,  and  the  silica  in  small,  sharp 
particles. 

Moisture. — Heat  2  grams  of  the  sample  at  105°  C.  for  two 
hours.  The  loss  will  be  moisture. 

Loss  on  Ignition. — Ignite  2  grams  of  the  sample  in  a  plati- 
num crucible  for  one  hour.  The  loss  will  be  water,  unless  a 
large  amount  of  carbonate  is  present. 

Complete  Analysis. — One-half  a  gram  of  the  sample  is  thor- 
oughly mixed  with  10  grams  of  sodium  carbonate,  and  1/2  gram 
of  potassium  nitrate,  in  a  platinum  crucible,  and  fused  until  clear. 
Cool,  dissolve  in  water  in  a  casserole.  Make  acid  with  hydro- 
chloric acid,  having  the  casserole  covered  with  a  watch  glass. 
Carefully  clean  out  the  crucible  with  a  little  acid,  adding  this  acid 
to  the  main  solution.  After  effervescence  has  ceased,  evaporate  to 
dryness  on  the  sand  bath.  Cool,  moisten  the  residue  with  a  few 

*  Treadwell  and  Hall,  analytical  chemistry,  Vol.  II,  page  491. 


24  ANALYSIS    OF    PAINTS   AND    PAINTING    MATERIALS. 

drops  of  hydrochloric  acid,  and  repeat  the  evaporation  to  dryness. 
Add  a  few  c.c.  of  concentrated  hydrochloric  acid,  allow  to  stand 
for  a  few  minutes,  and  add  about  10  c.c.  of  hot  water.  Filter, 
ignite,  and  weight  as  silica.  This  residue,  after  weighing,  should 
be  treated  with  an  excess  of  hydrofluoric  acid  and  a  few  drops 
of  sulphuric  acid.  Evaporate  to  dryness  and  ignite.  The  loss 
will  be  silica.  Any  residue  which  remains  in  the  crucible  should 
be  again  fused  with  sodium  carbonate  and  the  fusion  added  to 
the  original  nitrate.  If  barytes  is  found  to  be  present,  the  origi- 
nal sodium  carbonate  fusion  is  dissolved  in  hot  water  and  the 
barium  carbonate  filtered  off,  dissolved  in  hydrochloric  acid,  and 
precipitated  as  barium  sulphate  in  the  usual  way.  This  nitrate 
is  then  added  to  the  original  solution  and  the  silica  then  dehy- 
drated. The  iron  oxide  and  aluminum  oxide  are  precipitated 
in  the  nitrate  with  ammonium  hydroxide,  washed  and  weighed 
in  the  usual  way.  The  precipitate  of  iron  and  aluminum  oxides 
is  fused  in  a  platinum  crucible  with  potassium  acid  sulphate  solu- 
tion, the  fusion  taken  up  with  water,  treated  with  concentrated 
sulphuric  acid,  and  the  iron  titrated,  after  being  reduced  with  zinc, 
by  means  of  potassium  permanganate.  The  difference  between 
this  iron  oxide  and  the  combined  weight  of  iron  and  aluminum 
oxide  is  the  alumina.  The  filtrate  from  the  iron  and  aluminum- 
precipitation  is  treated  with  ammonium  oxalate,  and  the  calcium 
determined  as  described  .under  gypsum.  The  filtrate  from  the 
calcium  is  tested  for  magnesium  with  sodium  hydrogen  phos- 
phate, and  determined  in  the  usual  way.  Carbon  dioxide  pres- 
ent is  determined  in  a  separate  sample,  as  before  given.  The 
amount  found  is  calculated  to  calcium  carbonate.  Any  excess 
of  calcium  is  reported  as  oxide.  The  magnesium  is  calculated  as 
magnesium  oxide,  unless  the  carbon  dioxide  is  in  excess  of  the  cal- 
cium present,  in  which  case  it  is  calculated  to  magnesium  car- 
bonate, and  the  remainder  of  the  magnesium  to  the  oxide. 

Sodium  and  Potassium. — Mix  i  gram  of  the  sample  with 
one  part  of  ammonium  chloride  and  eight  parts  of  pure  calcium 
carbonate.  Heat  to  dull  redness  and  thus  convert  the  sodium  and 
potassium  to  chlorides.  Cool,  take  up  with  water.  Filter  and 
precipitate  the  calcium  with  ammonia  and  ammonium  oxalate, 
and  again  filter  and  wash.  Evaporate  to  dryness  in  a  weighed 
platinum  dish,  on  the  water  bath.  Take  care  to  avoid  spattering, 
as  dryness  is  reached.  Finally  heat  with  a  Bunsen  burner  to  a 


THE   ANALYSIS    OF    DRY    PIGMENTS.  25 

very  faint,  red  heat.  Cool  and  weigh.  This  weight  represents 
the  total  potassium  and  sodium  as  chlorides.  Take  up  the  resi- 
due in  water  and  add  an  excess  of  platinic  chloride  solution. 
Evaporate  to  small  volume,  take  up  with  80  per  cent,  alcohol,  filter 
in  a  Gooch  crucible,  wash  with  alcohol.  Dry  in  the  steam  oven. 
Calculate  the  potassium  in  the  potassium  platinic  chloride  to 
potassium  oxide  and  then  to  potassium  chloride.  The  difference 
between  the  potassium  chloride  and  the  combined  weight  of  the 
chlorides  is  the  sodium  chloride  which  may  then  be  calculated 
to  sodium  oxide.  It  is  well  to  convert  the  chlorides  of  sodium  and 
potassium  into  sulphate,  after  the  original  chloride  solution  has 
reached  a  small  volume,  by  the  addition  of  a  few  c.c.  of  sulphuric 
acid.  The  sulphates  of  these  metals  are  less  volatile  than  the 
chlorides,  and  greater  accuracy  can  be  obtained  by  this  method. 
After  weighing,  the  potassium  is  determined  as  before  stated. 

OCHERS,  UMBERS,  AND  SIENNAS. 

Mannhardt's*  method  for  the  determination  of  these  pigments 
is  an  excellent  one,  and  follows : 

"  One  gram  of  pigment  is  treated  with  20  c.c.  of  i  to  i  hydro- 
chloric acid  on  the  steam  plate  in  a  covered  beaker.  Small 
amounts  of  stannous  chloride  crystals  are  gradually  introduced 
into  the  hot  liquid  until  the  solution  and  insoluble  are  nearly 
colorless  and  the  iron  is  all  reduced  to  the  ferrous  state.  (In 
umbers,  which  all  contain  manganese,  this  should  be  removed 
as  MnO2.2H2O  by  boiling  with  excess  of  ammonium  hypo- 
bromite  in  ammoniacal  solution  before  taking  up  the  reduction 
with  stannous  chloride.)  The  ferrous  and  stannous  chloride 
solution  is  now  stirred  into  10  c.c.  of  6  per  cent,  solution  of 
mercuric  chloride  to  remove  the  stannous  salt.  An  equal  bulk 
of  strong  hydrochloric  acid  is  then  added  and  the  solution  titrated 
with  3  N/io  bichromate  using  a  pale  yellow  solution  of  ferri- 
cyanide  as  external  indicator.  Nearing  the  end  point,  more 
acid  is  added,  to  bring  the  solution  to  an  olive  color.  One  c.c. 
3  N/io  equals  .024  grams  Fe2O3.  Raw  siennas  may  contain  some 
ferrous  iron.  This  is  determined  by  dissolving  i  gram  of  pig- 
ment and  i  gram  of  bicarbonate  of  soda  with  hydrochloric  acid, 

*  Hans  Mannhardt,  Select  Methods  of  Paint  Analysis,  pp.  22  and  23. 


26  ANALYSIS    OF    PAINTS  AND    PAINTING    MATERIALS. 

using  a  small  flask  provided  with  a  Bunsen  valve.  The  ferrous 
iron  is  then  titrated  directly.  One  c.c.  3  N/io  equals  .0216  FeO. 

"The  hydrated  peroxide  of  manganese  is  best  determined 
as  manganous  pyrophosphate  Fresenius  Quant.,  Vol.  I,  page  297. 

"  The  complete  analysis  of  an  ocher,  umber,  or  sienna  requires 
the  fusion  method  of  solution.  In  the  interpretation  of  results 
any  alumina  is  calculated  to  clay  and  the  excess  silica  returned  as 
such.  The  loss  on  ignition  is  determined  on  a  separate  sample 
and  is  made  up  of  moisture  (organic  matter  sometimes),  the 
combined  water  of  the  clay,  and  the  combined  water  of  the 
limonite  2Fe2O3 .  3H2O.  The  Mn3O4  of  the  raw  umber  is  probably 
also  hydrated.  Burnt  ochers,  umbers,  and  siennas  of  course 
carry  very  little  free  and  combined  water." 

IRON  OXIDES. 

(Venetian  Red,  Metallic  Brown,  Indian  Red.) 

Test  for  free  sulphuric  acid,  by  boiling  in  water,  filtering  off 
and  using  litmus  paper.  Estimate  the  amount  -by  titration. 

Walker's*  method  for  the  analysis  of  oxide  and  earth  pig- 
ments, which  also  includes  the  analysis  of  ochers,  umbers,  and 
siennas,  is  as  follows : 

"  Iron  oxide  is  extensively  used  as  a  paint.  The  native  oxide 
naturally  varies  very  much  in  its  composition.  In  general, 
however,  only  the  poorer  grades  of  native  hematite  are  used  as 
paints.  Artificial  iron  oxide  pigments,  made  by  calcining 
copperas,  may  be  practically  pure  ferric  oxide.  Umbers,  ochers, 
and  siennas  are  earthy  substances  containing  iron  and  man- 
ganese oxides  and  more  or  less  organic  matter. 

"  The  methods  of  analysis  are  very  much  the  same  as  those 
for  iron  ores.  It  is  generally  sufficient  to  determine  moisture, 
loss  on  ignition,  insoluble  in  hydrochloric  acid,  ferric  oxide,  and 
manganese  dioxide.  If  much  organic  matter  is  present,  roast 
2.5  grams  in  a  porcelain  dish  at  a  low  temperature  until  all 
organic  matter  is  destroyed,  add  25  c.c.  of  hydrochloric  acid, 
cover  with  a  watch  glass,  and  heat  on  the  steam  bath  for  two 
hours;  then  add  10  c.c.  of  sulphuric  acid  (1:1),  evaporate,  and 

*  P.  H.  Walker.  Bulletin  No.  109,  revised,  Bureau  of  Chemistry, 
U.  S.  Dept.  of  Agriculture,  pp.  33  and  34. 


THE   ANALYSIS    OF    DRY   PIGMENTS.  27 

heat  until  fumes  of  sulphur  trioxide  are  evolved  and  all  the 
hydrochloric  acid  is  driven  off.  Cool,  add  50  c.c.  of  water,  boil 
until  all  of  the  iron  sulphate  is  dissolved,  filter  into  a  250  c.c. 
graduated  flask,  fill  to  the  mark,  mix,  and  take  out  a  portion  of 
50  c.c.  for  iron  determinations.  For  the  determination  of  iron 
reduce  with  zinc,  titrate  with  standard  potassium  permanganate, 
and  calculate  to  ferric  oxide.  For  the  determination  of  manga- 
nese transfer  100  c.c.  of  the  solution  (corresponding  to  i  gram) 
to  a  500  c.c.  flask,  add  sodium  hydroxide  solution  until  nearly 
but  not  quite  neutral.  Then  add  an  emulsion  of  zinc  oxide  in 
water  in  slight  excess,  shake  until  all  of  the  iron  is  thrown  down, 
fill  to  the  mark,  mix,  let  settle,  filter  through  a  dry  paper,  and  use 
portions  of  100  c.c.  (corresponding  to  0.2  gram)  for  the  manga- 
nese determination.  Transfer  to  a  300  c.c.  Erlenmeyer  flask, 
heat  to  boiling,  titrate  with  standard  permanganate.  The  flask 
must  be  shaken  during  the  titration  and  some  experience  is 
necessary  to  determine  the  end  point,  which  is  best  seen  by 
looking  through  the  upper  layer  of  liquid  and  observing  when  the 
pink  tinge  from  the  permanganate  does  not  disappear  on  shak- 
ing. A  standard  potassium  permanganate  solution,  the  iron 
factor  of  which  is  known,  may  be  used  to  determine  manganese. 
The  iron  factor  multiplied  by  o.  2952  gives  the  manganese  factor. 
In  some  cases  this  method  of  attack  will  not  separate  all  of  the 
iron  from  the  insoluble  matter.  In  such  a  case  the  insoluble 
must  be  fused  with  a  mixture  of  sodium  and  potassium  carbon- 
ates, dissolved  in  water,  evaporated  with  excess  of  sulphuric 
acid,  filtered  from  the  insoluble,  and  this  solution  added  to  the 
first  one. 

"  Another  method  is  as  follows :  Roast  5  grams  of  the  powder, 
digest  with  25  c.c.  of  hydrochloric  acid,  evaporate  to  dryness, 
moisten  with  hydrochloric  acid,  dissolve  in  water,  filter,  and 
wash  the  residue;  ignite  the  residue  in  a  platinum  crucible,  add 
sulphuric  acid  and  hydrofluoric  acid,  drive  off  the  latter,  and 
heat  until  copious  fumes  of  sulphuric  anhydride  come  off.  Add 
potassium  hydrogen  sulphate  and  fuse,  dissolve  in  water,  filter 
from  any  remaining  insoluble  (barium  sulphate),  unite  the  two 
solutions,  make  up  to  500  c.c.  and  use  aliquots  for  the  iron  and 
manganese  determinations.  For  the  determination  of  iron  place 
100  c.c.  in  a  flask,  add  about  3  grams  of  zinc,  put  a  funnel  into 
the  neck  of  the  flask,  heat  when  the  action  slackens;  if  basic 


28  ANALYSIS    OF    PAINTS  AND    PAINTING    MATERIALS. 

salts  separate  out  add  a  few  drops  of  hydrochloric  acid.  When 
all  of  the  iron  is  reduced,  add  30  c.c.  of  sulphuric  acid  (1:2),  and 
as  soon  as  all  of  the  zinc  is  dissolved  and  the  solution  is  cool, 
titrate  with  potassium  permanganate. 

"For  the  determination  of  manganese  use  50  c.c.,  evaporate 
to  a  very  small  bulk,  add  strong  nitric  acid  and  evaporate  the 
hydrochloric  acid;  add  75  c.c.  of  strong  nitric  acid,  which  should 
be  free  from  nitrous  acid,  and  5  grams  of  potassium  chlorate, 
heat  to  boiling  and  boil  fifteen  minutes;  then  add  50  c.c.  of 
nitric  acid  and  more  potassium  chlorate.  Boil  until  yellow 
fumes  cease  to  come  off,  cool  in  ice  water,  filter  on  asbestos,  and 
wash  with  colorless,  strong  nitric  acid;  suck  dry  and  wash  out 
remaining  nitric  acid  with  water,  transfer  the  precipitate  and 
the  asbestos  to  a  beaker,  add  a  measured  excess  of  standard 
solution  of  ferrous  sulphate  in  dilute  sulphuric  acid,  stir  until  all 
of  the  manganese  dioxide  is  dissolved,  and  titrate  the  remaining 
ferrous  sulphate  with  potassium  permanganate.  A  ferrous 
solution  of  about  the  proper  strength  is  made  by  dissolving  10 
grams  of  crystallized  ferrous  sulphate  in  900  c.c.  of  water  and 
100  c.c.  of  sulphuric  acid  (specific  gravity  i .  84) .  This  solution  is 
titrated  with  standard  potassium  permanganate.  The  reaction 
taking  place  when  the  manganese  dioxide  acts  on  the  ferrous 
sulphate  is  MnO2  +2FeSO4  +2H2SO4  =MnSO4  +Fe2(SO4)3  +H2O. 
Hence  the  iron  value  of  permanganate  multiplied  by  0.491  gives 
the  value  in  manganese." 

RED  LEAD  AND  ORANGE  MINERAL. 

"  These  pigments  in  the  pure  state  are  oxides  of  lead  (approxi- 
mately Pb3O4),  being  probably  mixtures  of  compounds  of  varying 
proportions  of  lead  monoxide  and  lead  dioxide.  Moisture, 
insoluble  impurities,  and  total  lead  may  be  determined  by  the 
methods  given  under  chrome  yellow;  or,  in  the  absence  of 
alkaline  earth  metals,  the  lead  may  be  determined  as  sulphate 
in  nitric  acid  solution  (dissolve  by  adding  a  few  drops  of  hydrogen 
dioxide)  by  evaporating  with  an  excess  of  sulphuric  acid  until 
fumes  of  sulphuric  anhydride  are  evolved.  Determine  as  sulphate 
in  the  usual  way. 

"The  lead  dioxide  (PbO2)  may  be  determined  as  follows: 
Weigh  0.5  gram  of  the  very  finely  ground  pigment  into  a  150  c.c. 


THE   ANALYSIS    OF    DRY   PIGMENTS.  2Q 

Erlenmeyer  flask.  Mix  in  a  small  beaker  15  grams  of  crystallized 
sodium  acetate,  1.2  grams  of  potassium  iodide,  5  c.c.  of  water, 
and  5  c.c.  of  50  per  cent,  acetic  acid.  Stir  until  all  is  liquid,  pour 
into  the  Erlenmeyer  flask  containing  the  lead,  and  rub  with  a 
glass  rod  until  all  of  the  lead  is  dissolved;  add  15  c.c.  of  water, 
and  titrate  with  tenth-normal  sodium  thiosulphate,  using  starch 
as  indicator.  A  small  amount  of  lead  may  escape  solution  at 
first,  but  when  the  titration  is  nearly  complete  this  may  be 
dissolved  by  stirring.  The  reagents  should  be  mixed  in  the 
order  given,  and  the  titration  should  be  carried  out  as  soon  as 
the  lead  is  in  solution,  as  otherwise  there  is  danger  of  loss  of 
iodine.  One  cubic  centimeter  of  tenth-normal  sodium  thio- 
sulphate corresponds  to  0.011945  gram  of  lead  dioxide,  or 
0.034235  gram  of  red  lead  (Pb3O4). 

"  These  colored  lead  pigments  may  have  their  color  modified 
by  the  addition  of  organic  coloring  matters.  As  a  general  rule, 
such  adulteration  may  be  detected  by  adding  20  c.c.  of  95  per 
cent,  alcohol  to-2  grams  of  the  pigment,  heating  to  a  boil,  and 
allowing  to  settle.  Pour  off  the  alcohol,  boil  with  water,  and 
allow  to  settle,  then  use  very  dilute  ammonium  hydroxide.  If 
either  the  alcohol,  water,  or  ammonium  hydroxide  is  colored, 
it  indicates  organic  coloring  matter.  The  quantitative  deter- 
mination of  such  adulteration  is  difficult  and  must  generally  be 
estimated  by  difference." 

Vermilion. 

"  True  vermilion,  or,  as  it  is  generally  called,  English  vermilion, 
is  sulphide  of  mercury.  On  account  of  its  cost  it  is  rarely  used 
in  paints,  and  is  liable  to  gross  adulteration.  It  should  show 
no  bleeding  on  boiling  with  alcohol  and  water  and  no  free  sulphur 
by  extraction  with  carbon  disulphide.  A  small  quantity  mixed 
with  five  or  six  times  its  weight  of  dry  sodium  carbonate  and 
heated  in  a  tube  should  show  globules  of  mercury  on  the  cooler 
portion  of  the  tube.  The  best  test  for  purity  is  the  ash,  which 
should  be  not  more  than  one-half  of  i  per  cent.  Make  the 
determination  in  a  porcelain  dish  or  crucible,  using  2  grams  of 
the  sample.  Ash  in  a  muffle  or  in  a  hood  with  a  very  good  draft, 
as  the  mercury  fumes  are  very  poisonous.  It  is  seldom  necessary 
to  make  a  determination  of  the  mercury;  but  if  this  is  required, 


30  ANALYSIS    OF    PAINTS  AND    PAINTING    MATERIALS. 

it  may  be  determined  by  mixing  0.2  gram  of  the  vermilion  with 
o.  i  gram  of  very  fine  iron  filings,  or  better  "iron  by  hydrogen." 
Mix  in  a  porcelain  crucible  and  cover  with  a  layer  10  mm.  thick 
of  the  iron  filings,  place  the  crucible  in  a  hole  in  an  asbestos 
sheet  so  that  it  goes  about  half  way  through,  cover  with  a 
weighed,  well  fitting,  gold  lid  which  is  hollow  at  the  top,  fill 
this  cavity  with  water,  heat  the  crucible  for  fifteen  minutes 
with  a  small  flame,  keep  the  cover  filled  with  water,  cool,  remove 
the  cover,  dry  for  three  minutes  at  100°  C.,  and  thirty  minutes 
in  a  desiccator,  and  weigh.  The  increase  in  weight  is  due  to 
mercury.  The  mercury  can  be  driven  off  from  the  gold  by 
heating  to  about  450°  C.  A  silver  lid  may  be  used,  but  gold  is 
much  better. 

"  Another  method  is  to  place  in  the  closed  end  of  a  combustion 
tube,  45  cm.  long  and  10  to  15  mm.  in  diameter,  a  layer  of  25  to 
50  mm.  of  roughly  pulverized  magnesite,  then  a  mixture  of 
10  to  15  grams  of  the  vermilion  with  four  or  five  times  its  weight 
of  lime,  followed  by  5  cm.  of  lime,  and  plug  the  tube  with  asbestos. 
Draw  out  the  end  of  the  tube  and  bend  it  over  at  an  angle  of 
about  60°.  Tap  the  tube  so  as  to  make  a  channel  along  the  top, 
and  place  it  in  a  combustion  furnace  with  the  bent  neck  down, 
resting  with  its  end  a  little  below  some  water  in  a  small  flask  or 
beaker.  Heat  first  the  lime  layer,  and  carry  the  heat  back  to 
the  mixture  of  lime  and  pigment.  When  all  the  mercury  has 
been  driven  off,  heat  the  magnesite,  and  the  evolved  carbon 
dioxide  will  drive  out  the  last  of  the  mercury  vapors.  Collect 
the  mercury  in  a  globule,  wash,  dry,  and  weigh. 

"  Genuine  vermilion  is  at  the  present  time  little  used  in  paints. 
Organic  lakes  are  used  for  most  of  the  brilliant  red,  scarlet,  and 
vermilion  shades.  These  organic  coloring  matters  are  some- 
times precipitated  on  red  lead,  orange  mineral,  or  zinc  oxide; 
but  as  a  usual  thing  the  base  is  barytes,  whiting,  or  china  clay. 
Paranitraniline  red,  a  compound  of  diazotized  paranitraniline  and 
beta-naphthol  is  largely  employed;  but  a  number  of  colors  may 
be  used.  To  test  for  red  colors  in  such  a  lake  the  following 
method  from  Hall*  may  be  of  value,  though  other  colors  may 
be  employed,  which  makes  the  table  of  only  limited  use. 

*  "The  Chemistry  of  Paints  and  Paint  Vehicles,"  p.  29. 


THE  ANALYSIS    OF    DRY    PIGMENTS. 


o 
a 

eS 

bJO 

O 
a 


LH 

LJ 

G 

r] 

JH 

£ 

£ 

O 

Cfl 

fn 

Q 

TH 

rG 

•42 

CD 

vp 

rS 

to    . 

be    . 

a 

rd 

^ 

3      . 

O 

Darkened;  li 
on  diluting 

Darkened;  li 
on  diluting 

Reddish  sol 

on  diluting 

•O 

rH 
-P 

02 

solution. 
Color  d  a  r 

reddish  sol 
on  diluting 

G 

rG        G 

cu 

0 

cfl    0 

G 

•rH 

• 

1 

?J3 

& 

i 

1 

'G 

bo 

S  .rt 

bJo 

2 

cd 

.-  ti 

O,""1 

o 

o 

6 

"     *4^ 

*^j 

CD 

fli 

ar3 

In    ^ 

J3 

^ 

4J 

s 

I5 

Q      *" 

-3 

3 

J 

. 

<u 

0)    +J 

£  ^ 

bb 

0 

if  ^ 

^ 

G    i 
.2    *" 

3 

| 

G 

g 
d 

§1 

'S     C 

bo  71. 

S 

T3 

CU 

to 

<H 

V    G 

rG        O 

CO 

1 

G 

<5 

i 

o 

o3 
£ 
G 
o3 
S 

urple;  c< 
turning  o 

bJD 
G 

olor  s  1  i 
darkened 

•3 

G 
o 

fe 

o3 
,G 
0 

u 

jO 

'o 

br  o  wni 
Light  red 

be 

li 

W3      O 

be  cb" 

.S   bb 

5  .S 

02 

OH 

dn 

O 

O 

""  02 

£ 

G 
cfl 

O 

Changes  to  yel- 
low; fluorescent 

solution  with 
excess  of  sodium 

hydroxide. 

Changes  to  yel- 
low; reddish 

fluorescent  solu- 
tion with  excess 

of  sodium  hy- 
droxide. 
Little  change; 

fluorescent  solu- 
tion on  diluting. 

Reddish  fluo- 

rescent  solution. 

+3    ^ 

G°  0 

cfl 

^ 

•^  ^S 

• 

^ 

4 

V3 

•p 

G 

'§    ^ 

oj 

S 

G 

^    * 

8  1 

0  _ 

O    "  . 

•d 

^     0 

G 

'S 

N 

^3 

11 

Q   * 

li 

diluting. 

11 

O   : 

o 

t-i 

(H 

Q 

brown; 
change 

luting. 
Insoluble 

Purplish; 

0 

i 

l.s 

•0 

12" 

0) 

4) 

*2 

•g 

*2 

crt 

*fl 

'S 

CU 

o 

0 

• 

j 

TO 

0 

tH 

H 

T3 

5 

1 

^ 

"o 

^ 

G 

P 

f 

tj 

'C 
S    o 
.G    C 

1  s 

| 

\ 

3 

a 
^ 

ii 

i  s 

•3 

o 

0 

*§ 
o 

8  8 

o 

o 

02 

w  - 

02 

"^ 

02 

32  ANALYSIS    OF   PAINTS  AND   PAINTING    MATERIALS. 

"It  is  well  also  to  try  the  action  of  reducing  and  oxidizing 
agents  such  as  stannous  chloride,  ferric  chloride,  etc.  (See  Zerr, 
Bestimmung  von  Teerfarbstoffen  in  Farblacken;  also  Schultz 
and  Julius,  A  Systematic  Survey  of  the  Organic  Coloring  Mat- 
ters.) 

"  Paranitraniline  red  is  soluble  in  chloroform.  It  is  also  well 
to  try  the  solvent  action  on  different  reds,  of  sodium  carbonate, 
etc.  The  amount  of  organic  pigment  present  in  such  reds  is 
generally  very  small,  and  when  it  cannot  be  determined  by 
ignition  owing  to  the  presence  of  lead,  zinc,  or  carbonate,  it  is  best 
determined  by  difference."* 

BLUE  PIGMENTS. 

The  only  two  blue  pigments  which  come  into  great  use  in 
the  paint  trade  are  Ultramarine  and  Prussian  blue. 

Ultramarine  Blue. 

Ultramarine  blue  is  formed  by  burning  together  silicates, 
aluminates,  sulphur,  charcoal,  and  soda.  Although  of  indefinite 
composition,  it  is  essentially  a  silicate  and  sulphide  of  sodium  and 
aluminum.  This  compound  may  be  identified  by  its  evolution  of 
hydrogen  sulphide  when  treated  with  acid.  Although  seldom 
used  in  the  paint  trade,  if  an  analysis  is  desired,  it  may  be  carried 
out  in  the  following  way. 

Moisture. — Heat  2  grams  of  the  sample  at  105°  C.  for  two 
hours.     The  loss  will  be  moisture. 

Silica. — One  gram  of  the  sample  is  digested  with  20  c.c. 
dilute  hydrochloric  acid  to  complete  decomposition,  taking 
care  to  avoid  spattering.  Evaporate  to  dryness,  dehydrate, 
cool,  moisten  with  a  few  drops  of  concentrated  hydrochloric  acid. 
Repeat  the  evaporation  and  dehydration,  cool,  moisten  with  a 
few  c.c.  concentrated  hydrochloric  acid,  dilute  with  hot  water, 
filter,  and  weigh  the  insoluble  residue.  Treat  the  contents  of 
the  crucible  with  an  excess  of  hydrofluoric  acid  and  a  few  drops 
of  sulphuric  acid,  evaporate  to  dryness,  and  ignite.  The  loss 
will  be  silica.  Any  residue  remaining  after  this  treatment  should 
be  examined. 

Alumina. — The  filtrate  from  the  silica  is  treated  with  ammo- 

*  Bulletin  109,  revised,  Bureau  of  Chemistry,  U.  S.  Dept.  of  Agri- 
culture, pp.  31,  32  and  33. 


THE   ANALYSIS    OF    DRY   PIGMENTS.  33 

nium  hydroxide  until  faintly  alkaline.  The  aluminum  hy- 
droxide precipitated  is  filtered,  washed,  and  weighed  as  A12O3. 
If  iron  is  present  it  may  be  separated  from  alumina  by  the 
fusion  method  as  stated  under  the  analysis  of  white  pigments. 

Sodium  Oxide. — Treat  the  filtrate  after  the  removal  of  the 
aluminum  with  sulphuric  acid  until  faintly  acid.  Evaporate 
to  dryness,  weigh  the  sodium  sulphate  in  a  weighed  dish.  Should 
calcium  be  present,  the  sodium  is  determined  in  the  filtrate  after 
the  removal  and  determination  of  the  calcium  as  oxalate,  in  the 
way  previously  stated. 

Total  Sulphur. — One  gram  of  the  sample  is  fused  with  a  mix- 
ture of  potassium  nitrate  and  sodium  carbonate.  Dissolve  the 
fused  mass  in  hydrochloric  acid  and  boil,  after  the  addition  of 
concentrated  nitric  acid.  Filter  off  the  insoluble  residue.  Deter- 
mine the  sulphate  in  the  filtrate  in  the  usual  way,  by  precipita- 
tion as  barium  sulphate  with  barium  chloride.  The  sodium 
peroxide  method  for  the  oxidation  of  sulphur  is  often  used  for 
this  determination. 

Sulphur  Present  as  Sulphate. — One  gram  of  the  sample  is 
boiled  with  dilute  hydrochloric  acid  until  all  the  hydrogen 
sulphide  has  been  driven  off.  Filter  and  wash  the  insoluble 
residue  with  hot  water,  precipitate  the  sulphur  present  in  the 
filtrate,  as  usual.  The  amount  of  the  sulphate  present  is  deducted 
from  the  total  sulphur  found  as  sulphate  by  the  fusion  method, 
— the  difference  calculated  to  sulphur  and  reported  as  such. 

Ultramarine  blues  usually  vary  between  the  following  limits: 

Sulphur,  10  to  14  per  cent. 

Sulphur  trioxide,  2  to     5  per  cent. 

Alumina,  20  to  27  per  cent. 

Silica,  39  to  45  per  cent. 

Soda,  15  to  20  per  cent. 

Prussian  Blue  (Antwerp  Blue  and  Chinese  Blue  *) . 

This  pigment  is  a  double  iron  and  potassium  salt  of  hydro- 
ferricyanic  and  hydroferrocyanic  acids.  Its  composition  is  rather 
indefinite  and  consequently  analyses  of  the  compound  give  varied 
results.  The  following  method  of  analysis  has  been  much  used 
by  the  authors : 

*  Chinese  Blue  often  contains  a  small  percentage  of  tin  salts.  They 
should  be  looked  for  in  the  qualitative  examination. 

3 


34  ANALYSIS    OF    PAINTS   AND    PAINTING    MATERIALS. 

Moisture. — Two  grams  of  the  sample  are  heated  at  105°  C. 
for  two  hours.  The  loss  will  be  moisture.  Less  than  7  per 
cent,  moisture  should  be  present  in  dry  Prussian  blue. 

Iron  and  Aluminum  Oxides. — One  gram  of  the  sample  is 
ignited  at  a  low  temperature  until  the  last  trace  of  blue  has  been 
decomposed.  The  ignition  must  be  low,  so  as  to  prevent  any 
iron  from  being  rendered  difficultly  soluble  in  hydrochloric 
acid.  After  cooling,  treat  the  mass  with  25  c.c.  hydrochloric 
acid  i :  i  and  digest  for  one  hour.  No  residue  will  remain  if  a 
pure  Prussian  blue  is  being  examined.  In  some  instances  a  resi- 
due does  remain  after  this  treatment,  due  to  the  presence  of 
inert  bases  upon  which  the  blue  has  been  precipitated,  such  as 
barytes.  Should  such  an  insoluble  residue  be  present,  evaporate 
the  solution  to  dryness,  take  up  with  hot  water  and  dilute 
hydrochloric  acid,  boil,  filter,  wash,  and  weigh  the  insoluble  resi- 
due. Examine  this  for  silica,  barium  sulphate,  and  alumina. 

The  filtrate  from  the  last  treatment,  or  the  original  solution, 
should  no  insoluble  matter  be  present,  is  divided  into  aliquot 
portions.  One  of  these  portions  is  made  faintly  acid  with 
ammonium  hydroxide  and  the  combined  aluminum  and  iron 
hydroxides  formed  filtered,  washed,  and  weighed  in  the  usual 
way.  The  iron  may  be  determined  in  the  combined  oxides 
by  fusion  with  potassium  acid  sulphate  and  titration  with 
potassium  permanganate  in  the  usual  way.  The  filtrate  should 
be  examined  for  calcium  present  as  calcium  sulphate. 

Nitrogen. — Nitrogen  is  determined  by  the  Kjehdahl-Gunning 
method. 

Commercial  Method. — According  to  Parry  and  Coste,*  the 
percentage  of  Prussian  blue  can  be  determined  with  sufficient 
accuracy  for  commercial  purposes  by  multiplying  the  percentage 
of  nitrogen  by  4.4  and  the  percentage  of  iron  by  3.03.  The 
iron  in  this  case  may  be  titrated  directly  after  solution  in  hydro- 
chloric acid. 

Akalies  and  Sulphuric  Acid. — Alkaline  salts  are  estimated 
in  the  filtrate  after  the  removal  of  calcium,  in  the  usual  way 
One  of  them  only  will  usually  be  present.  Calculate  to  metal, 
then  to  sulphate,  accounting  for  all  the  sulphuric  acid  as  alka- 
line sulphate. 

Sulphuric  acid  is  determined  in  the  other  aliquot  portion,  by 

*  The  Analyst,  1896,  21,  225  to  230. 


THE   ANALYSIS    OF    DRY    PIGMENTS.  35 

precipitation    as    barium    sulphate,    in    the    usual    way.     It   is 
calculated  to  alkaline  sulphate. 


Yellow    and    Orange    Pigments    (American   Vermilion,    Chrome 
Yellow,  Lemon  Chrome,  and  Orange  Chrome). 

The  above  pigments,  varying  in  color,  always  contain 
chromates.  The  light  colored  pigments  usually  contain  lead 
sulphate  or  other  insoluble  lead  compounds.  The  darker 
pigments  sometimes  contain  basic  lead  chromate.  It  is  advisable 
to  treat  the  pigment  with  alcohol  to  determine  the  presence  of 
any  organic  coloring  matter.  Pure  chrome  yellow  should 
contain  only  lead  chromate  and  insoluble  lead  compounds. 
These  pigments  are  analyzed  in  the  following  way: 

Moisture. — Heat  2  grams  of  the  sample  at  105°  C.  for  two 
hours.  Loss  will  be  moisture. 

Insoluble  Residue. — One  gram  of  the  sample  is  treated  with 
25  c.c.  concentrated  hydrochloric  acid,  the  solution  boiled, 
during  which  a  few  drops  of  alcohol  are  added  one  at  a  time. 
Dilute  to  100  c.c.  with  hot  water,  continue  the  boiling  for  ten 
minutes,  filter,  wash,  weigh  the  insoluble  residue.  This  residue 
is  examined  for  silica,  barium  sulphate,  and  alumina. 

Lead. — After  neutralizing  the  greater  portion  of  the  acid 
present  with  ammonium  hydroxide,  after  the  removal  of  the 
insoluble  residue,  the  solution  is  diluted  to  about  300  c.c.  with 
water.  Precipitate  the  lead  completely  with  hydrogen  sulphide, 
allow  to  settle,  evaporate,  wash  with  hydrogen  sulphide  water. 
Dissolve  the  lead  sulphide  in  hot  dilute  nitric  acid,  add  an 
excess  of  sulphuric  acid,  evaporate  until  heavy  fumes  of  sul- 
phuric acid  are  given  off,  cool,  dilute  with  water,  add  an  equal 
volume  of  alcohol,  filter,  determine  the  lead  either  volumetrically 
or  gravimetrically,  as  given  under  White  Lead. 

Chromium. — The  filtrate  from  the  lead  precipitate  is  boiled 
until  all  the  hydrogen  sulphide  is  expelled.  Precipitate  the 
chromium  as  chromium  hydroxide  with  ammonium  hydroxide, 
observing  the  usual  precautions  for  preventing  the  precipitation 
of  any  zinc.  Filter,  wash,  and  weigh  as  chromic  oxide.  Cal- 
culate to  chromic  anhydride. 

Zinc. — Precipitate  the  zinc  in  the  filtrate  from  the  chromium 
precipitation,  with  hydrogen  sulphide,  as  given  under  Zinc 


36  ANALYSIS    OF    PAINTS   AND    PAINTING    MATERIALS. 

Oxide,  filter,  wash,  and  weigh.  Determine  the  zinc  either 
gravimetrically  or  volumetrically,  as  before  outlined. 

Calcium  and  Magnesium. — Determine  the  calcium  and 
magnesium  in  the  filtrate  in  the  usual  way. 

Sulphuric  Acid. — The  combined  sulphate  is  estimated  by 
dissolving  i  gram  of  the  sample  in  hydrochloric  acid,  removing 
the  insoluble  residue  by  filtration,  precipitating  as  barium 
sulphate,  in  the  usual  way.  The  barium  sulphate  precipitated 
will  be  pure,  providing  the  solution  is  kept  dilute  and  hot, 
otherwise  lead  sulphate  may  be  precipitated.  Should  the 
precipitate  become  contaminated,  the  sulphate  is  best  determined 
by  the  Hughes  method,  as  outlined  on  page  17. 


GREEN  PIGMENTS. 

(Chrome  Green.) 

The  green  pigments  which  are  of  most  importance  are  those 
consisting  of  a  mixture  of  Prussian  blue  and  chrome  yellow. 
Organic  colors  are  sometimes  used  to  give  the  pigment  a  bright 
tint.  It  is- well  to  examine  all  green  pigments  for  coloring  mat- 
ter by  boiling  with  alcohol. 

Owing  to  the  various  composition  of  greens,  due  to  the  method 
of  manufacture,  a  chemical  examination  is  attended  with  many 
difficulties,  and  in  many  cases  is  of  small  value  in  determining 
the  true  value  of  the  green.  The  usual  methods  of  color  assay 
for  strength,  by  mixing  with  a  weighed  portion  of  white-base 
pigment  and  observing  the  tint  produced,  should  be  made. 
The  pigment  should  also  be  carefully  examined  by  means  of  the 
microscope,  so  as  to  determine  whether  the  green  is  a  product 
made  by  precipitating  the  two  pigments  together  or  by  mixing 
the  blue  and  yellow  pigments  after  separate  precipitation.  The 
former  have  the  greater  value.  A  good  green  will  show  the 
presence  of  green  and  blue  particles  but  no  yellow,  while  a  poor 
green  will  show  yellow  and  blue  particles  mixed  with  green. 
Analysis  of  the  green  may  be  made  in  the  following  way : 

Moisture. — Heat  2  grams  of  the  sample  at  105°  C.  for  two 
hours.  The  loss  will  be  moisture. 

Insoluble  Residue. — One  gram  of  the  sample  is  heated  at  a 
very  low  heat  in  a  casserole  until  the  blue  color  has  been  com- 


THE   ANALYSIS    OF    DRY    PIGMENTS.  37 

pletely  destroyed,  keeping  the  temperature  sufficiently  low  so  as 
not  to  render  any  of  the  iron  or  lead  chromates  insoluble.  Cool, 
add  30  c.c.  of  concentrated  hydrochloric  acid,  boil  until  all  the 
soluble  constituents  have  passed  into  solution.  This  can  be 
hastened  by  the  addition  of  a  few  drops  of  alcohol  added  one  at 
a  time.  Dilute  with  water,  boil,  filter,  wash,  and  weigh  the 
insoluble  residue.  This  residue  is  then  carefully  examined  for 
silica,  barytes,  and  occasionally  alumina  in  the  manner  given 
under  the  analysis  of  a  white  pigment. 

Lead. — The  excess  of  acid  present  in  the  nitrate  from  the  in- 
soluble residue  is  neutralized  with  ammonia  until  barely  acid. 
Dilute  to  300  c.c.,  allow  to  cool,  and  treat  with  hydrogen  sul- 
phide until  the  lead  sulphide  is  completely  precipitated.  Allow 
the  precipitate  to  settle,  filter,  wash,  dissolve  in  nitric  acid, 
determine  the  lead  as  described  under  the  analysis  of  yellow 
pigments. 

Iron,  Alumina,  and  Chromium. — The  filtrate  from  the  lead 
precipitate  is  boiled  until  all  the  hydrogen  sulphide  has  been 
expelled.  Add  a  few  drops  of  nitric  acid,  boil  for  a  few  minutes 
to  complete  oxidation  of  the  iron,  precipitate  the  iron,  alumina,  • 
and  chromium  as  hydroxides  with  ammonium  hydroxide. 
This  precipitate  is  filtered  off,  washed,  and  dissolved  in  hydro- 
chloric acid  and  made  up  to  a  definite  volume.  In  one  portion 
the  iron,  aluminum,  and  chromium  hydroxides  are  precipitated 
with  ammonium  hydroxide,  filtered,  washed,  and  weighed  to- 
gether. Another  portion  is  treated  in  a  flask  with  an  excess  of 
potassium  hydroxide  and  bromine  water  until  the  iron  hydroxide 
has  assumed  its  characteristic  reddish  brown  color.  Dilute 
with  water,  filter,  and  wash.  Dissolve  the  iron  hydroxide  in 
hydrochloric  acid  and  determine  the  iron  in  the  solution  either 
volumetrically  or  gravimetrically,  as  stated  under  the  analysis 
of  iron  oxides.  The  filtrate  from  the  iron  precipitate  is  made 
acid  with  nitric  acid,  and  the  alumina  precipitated  and  deter- 
mined in  the  usual  way  by  precipitation  with  ammonium  hy- 
droxide. Chromium  is  determined  in  the  filtrate  by  reduction 
to  a  chromic  salt  with  hydrochloric  acid  and  alcohol,  precipitated 
with  ammonium  hydroxide  and  weighed  as  oxide. 

Calcium  and  Magnesium. — Calcium  and  magnesium  are 
determined  in  the  filtrate  from  the  iron,  alumina,  and  chromium 
precipitation. 


38  ANALYSIS    OF    PAINTS  AND    PAINTING    MATERIALS. 

Sulphuric  Acid. — One  gram  of  the  sample,  after  ignition  until 
the  blue  is  completely  decomposed,  as  before  stated,  is  dissolved 
in  30  c.c.  of  concentrated  hydrochloric  acid,  diluted  with  water, 
boiled,  filtered,  and  washed.  Determine  the  barium  sulphate 
in  the  usual  way. 

Nitrogen. — Nitrogen  is  determined  as  stated  under  the 
analysis  of  Prussian  blue. 

Interpretations  of  Results. — The  Prussian  blue  present  is 
determined  by  multiplying  the  iron  found  by  3.03  or  the  nitro- 
gen found  by  4.4.  The  sulphate  is  calculated  to  lead  sulphate 
and  calcium  sulphate,  should  calcium  be  present,  and  the 
chromium  to  lead  chroma te. 


BLACK  PIGMENTS    (Bone    Black,    Drop   Black,    Ivory   Black, 
Lampblack,  Mineral  Black,  Graphite). 

The  usual  black  pigments  are  those  consisting  of  carbon, 
existing  either  in  the  crystalline  form  (graphite)  or  the  amorphous 
form  which  includes  all  the  many  artificial  carbon  blacks.  Many 
paints  are  made  at  the  present  time  from  coal-tar  and  asphaltic 
mixtures,  and  it  is  deemed  advisable  to  treat  of  these,  owing  to 
many  difficulties  attending  their  analysis,  under  a  separate  chap- 
ter. For  the  analysis  of  simple  black  pigments  the  following 
method  will  be  found  to  embrace  all  the  essential  points  needed 
for  their  examination.  An  extraction  of  the  black  pigment 
should  be  made  with  ether  to  determine  the  presence  of  oil. 
If  present,  it  may  be  determined  gravimetrically  in  a  fat  extrac- 
tion apparatus. 

Moisture. — Dry  2  grams  of  the  sample  at  105°  C.  for  two 
hours.  Loss  will  be  moisture. 

Volatile  Matter. — One  gram  of  the  sample  is  heated  in  a  large 
covered  crucible  with  a  Bunsen  burner  for  ten  minutes.  The 
loss  will  be  volatile  matter. 

Ash. — Two  grams  of  the  sample  are  ignited  at  a  bright  red 
heat  until  the  carbon  has  all  been  driven  off.  The  residue  will 
be  ash.  Should  the  black  pigment  consist  of  graphite,  the 
ignition  must  be  made  with  the  aid  of  oxygen.  Ignite  until  all 
the  carbon  is  burned  off  and  report  as  carbon.  Should  carbonates 
be  present,  the  ash  is  mixed  with  a  small  amount  of  ammonium 
carbonate  and  again  ignited  and  weighed.  This  will  reconvert 


THE   ANALYSIS    OF    DRY   PIGMENTS.  39 

any  carbonates  which  may  have  been  converted  to  oxides  on 
ignition. 

Soluble  Salts. — The  ash  from  the  above  is  boiled  with  con- 
centrated hydrochloric  acid,  diluted  with  water,  again  boiled, 
filtered,  and  the  insoluble  residue  weighed.  Should  it  be 
desired,  the  insoluble  residue  may  be  examined  for  silica,  barium 
sulphate,  and  alumina.  The  nitrate  is  examined  for  phosphoric 
acid,  calcium,  and  magnesium. 


CHAPTER  II. 
THE  ANALYSIS  OF  MIXED  PIGMENTS  AND   PAINTS. 

After  making  the  usual  observations  as  to  the  statements  on 
the  label  of  the  can,  gross  weight  of  package,  etc.,  the  can  is 
opened,  and  the  material  well  stirred,  preferably  by  transferring 
the  entire  contents  to  a  large  receptacle.  A  uniform  sample  is 
then  withdrawn  for  analysis.  The  original  can  may  be  cali- 
brated by  pouring  in  a  standard  volume  of  water. 

A  portion  (about  15  grams)  of  the  sample  of  paint  withdrawn 
for  analysis  is  weighed  into  a  2 -ounce  tared  centrifuge  bottle, 
and  40  c.c.  of  a  vehicle  solvent*  added.  The  bottle  is  then 
capped  and  placed  in  the  centrifuge  machine  for  twenty  minutes, 
when  it  is  removed  and  the  vehicle  poured  off  from  the  settled 
pigment.  Successive  portions  of  solvent  are  again  added,  and 
the  operation  repeated  several  times  until  the  pigment  has  been 
thoroughly  extracted.  The  bottle  and  its  contents  of  pigment 
is  dried  at  105°  C.  in  an  air-bath,  and,  after  weighing,  the  loss  is 
calculated  to  the  percentage  of  vehicle  in  the  paint,  the  balance 
being,  of  course,  pigment. 

The  dried  pigment  is  now  ready  for  analysis. 

GENERAL  METHODS  FOR   THE   ANALYSIS   OF   A   MIXED 
WHITE  PAINT. 

Any  of  the  constituents  mentioned  under  the  analysis  of 
simple  white  pigments  may  be  present  in  a  mixed  white  paint. 
The  analysis  may  be  considerably  shortened  by  a  preliminary 
qualitative  examination.  It  is  assumed,  however,  that  zinc  sul- 
phide will  not  be  present  with  lead  compounds,  as  such  a  mixture 
is  apt  to  blacken.  Either  of  the  following  general  methods  may 
be  used  in  such  an  analysis. 

Method  i. — One  gram  of  the  dry  pigment  is  treated  with  20 
c.c.  (i :  i)  hydrochloric  acid.  Evaporate  to  dryness,  moisten 
with  a  few  cubic  centimeters  of  concentrated  hydrochloric  acid, 

*  50  parts  benzol,  40  parts  wood  alcohol,  10  parts  acetone. 

40 


THE   ANALYSIS    OF    MIXED    PIGMENTS   AND    PAINTS.  41 

allow  to  stand  for  several  minutes,  dilute  to  100  c.c.  with  hot 
water,  boil,  filter,  and  wash  the  insoluble  residue  with  hot  water. 
It  is  advisable  to  treat  the  residue  after  washing  into  the  original 
beaker  with  i :  i  hydrochloric  acid  and  2  c.c.  of  dilute  sulphuric 
acid.  Boil,  filter  and  wash.  This  will  usually  remove  the  last 
traces  of  lead.  Should  TIO  barium  sulphate  be  present,  the 
hydrochloric  acid-sulphuric  acid  treatment  may  be  used  in  the 
first  instance.  The  insoluble  residue  is  ignited  and  weighed. 
After  weighing,  treat  the  contents  of  the  crucible  with  an  excess 
of  hydrofluoric  acid  and  a  few  drops  of  sulphuric  acid.  Evapo- 
rate to  dryness  and  ignite.  The  loss  will  be  silica. 

The  residue,  after  the  silica  has  been  removed  by  volatiliza- 
tion, is  fused  with  potassium  acid  sulphate,  and  the  melt  taken 
up  in  hot  water.  Filter,  wash,  and  weigh,  as  given  under  Barium 
Sulphate.  The  filtrates  from  the  original  fusion  and  extraction 
are  then  combined.  A  sodium  carbonate  fusion  may  also  be 
resorted  to  in  place  of  potassium  acid  sulphate  at  this  point. 

Warm  the  combined  filtrates  and  pass  in  hydrogen  sulphide 
until  the  lead  is  completely  precipitated,  having  from  3  to  4  i  /2 
c.c.  of  concentrated  hydrochloric  acid  for  every  100  c.c.  of  neu- 
tral solution.  If  the  color  of  this  precipitate  is  gray,  it  is  a 
sign  that  some  zinc  is  being  precipitated,  and  acid  must  be 
added.  Should  the  precipitate  be  reddish-black,  the  solution 
is  too  acid.  Cool  the  contents  of  the  beaker,  filter,  and  wash. 
The  lead  is  estimated  as  described  under  Basic  Carbonate  White 
Lead.  Boil  the  filtrate  from  the  lead  precipitate  until  the  hy- 
drogen sulphide  is  completely  removed.  Add  a  lew  drops  of 
nitric  acid,  ammonium  chloride,  and  .ammonium  hydroxide  to 
faint  excess.  Filter,  wash,  and  weigh  the  aluminum  oxide  and 
any  iron  oxide  which  is  precipitated  in  the  usual  way,  observing 
the  usual  precautions  to  prevent  the  precipitation  of  zinc. 
Should  the  residue  be  colored,  indicating  the  presence  of  iron, 
the  iron  oxide  may  be  separated  from  the  alumina  by  fusion 
with  potassium  acid  sulphate.  Take  up  the  fusion  with  water, 
acidify  with  sulphuric  acid,  reduce  with  zinc,  and  titrate  in  the 
usual  way  with  potassium  permanganate.  Calculate  to  Fe2O3. 
The  difference  between  this  and  the  total  oxides  will  be  A12O3. 
The  amount  of  iron  oxide  present  in  the  case  of  white  pigments 
will  be  in  most  cases  inappreciable.  Acidify  the  filtrate  from 
the  iron  oxide  and  alumina  faintly  with  acetic  acid  and  heat  to 


42  ANALYSIS    OF    PAINTS   AND    PAINTING    MATERIALS. 

boiling.  Saturate  with  H2S  and  boil  for  ten  minutes.  Deter- 
mine the  zinc  either  gravimetrically  or  volumetrically,  as  under 
Zinc  Oxide.  To  the  bo  ling  alkaline  filtrate  add  boiling  ammon- 
ium oxalate,  and  determine  the  calcium  in  the  usual  way.  Pre- 
cipitate the  magnesium  in  the  filtrate  with  sodium  hydrogen 
phosphate  and  determine  in  the  usual  way. 

Barium  carbonate  is  sometimes  found  in  mixed  paints,  and 
it  is  well  to  test  for  this  before  the  precipitation  of  calcium.  A 
relatively  large  percentage  of  magnesium  denotes  the  presence  of 
asbestine. 

The  calculation  of  aluminum  oxide  to  clay  and  determination 
of  the  silica  present  is  carried  out,  according  to  Scott,  as  follows: 

Weight  of  A12O3  X2  . 5372  =  Weight  of  clay. 
Weight  of  Clay  X  .  4667  =  Weight  of  SiO2  in  clay. 

Any  difference  greater  than  5  per  cent,  may  be  considered 
silica. 

Estimation  of  SO4  in  the  lead  sulphate  which  may  be  present. 
Treat  i  gram  of  the  sample  with  200  c.c.  of  water  and  dilute 
hydrochloric  acid.  Add  several  pieces  of  spongy  zinc  and  boil. 
After  complete  precipitation  of  the  lead,  filter  and  wash.  Pre- 
cipitate the  sulphuric  acid  in  the  usual  way,  as  barium  sulphate. 
Filter,  wash,  and  weigh.  Calculate  the  SO4  to  lead  sulphate. 

Method  2. — The  second  method  depends  upon  the  sepa- 
ration of  the  compounds  soluble  in  acetic  acid  from  the  in- 
soluble compounds. 

Moisture. — Dry  2  grams  of  the  sample  at  105°  C.  for  two 
hours.  The  loss  will  be  moisture. 

Residue  Insoluble  in  Acetic  Acid. — One  gram  of  the  sample 
is  boiled  with  a  mixture  of  10  c.c.  95  per  cent,  acetic  acid  and 
25  c.c.  of  water.  Filter  and  wash  the  insoluble  residue.  The 
filtrate  is  carefully  preserved  for  quantitative  examination. 
The  insoluble  residue,  after  washing  into  a  beaker,  is  treated  with 
25  c.c.  of  hydrochloric  acid  (1.2)  and  5  grams  of  ammonium 
chloride.  Heat  on  the  steam-bath  for  a  few  minutes,  dilute 
with  hot  water  to  about  300  c.c.,  boil,  filter,  wash,  and  weigh 
the  insoluble  residue.  This  residue  is  examined  for  silica, 
aluminum,  and  barium  sulphate,  as  stated  under  the  first  method 
for  the  general  analysis  of  pigments.  The  lead  is  precipitated 
in  the  filtrate  in  the  usual  way  with  hydrogen  sulphide.  The 


THE   ANALYSIS    OF    MIXED    PIGMENTS   AND    PAINTS.  43 

lead  sulphide  precipitate  is  filtered,  washed,  dissolved  in  nitric 
acid,  evaporated  in  the  presence  of  sulphuric  acid,  and  deter- 
mined either  gravimetrically  or  volumetrically,  as  stated  under 
Basic  Carbonate- White  Lead.  The  lead  found  is  calculated  to 
lead  sulphate.  The  filtrate  from  the  lead  precipitate  is  examined 
for  aluminum  and  calcium  in  the  usual  way.  Any  calcium  is 
calculated  to  calcium  sulphate. 

Compounds  Soluble  in  Acetic  Acid. — The  filtrate  from  the 
acetic  acid  treatment  may  contain  lead,  zinc,  barium,  calcium 
and  magnesium.  The  zinc  and  lead  are  removed  by  passing 
hydrogen  sulphide  into  the  hot  solution  until  completely  pre- 
cipitated. Filter,  wash,  dissolve  in  nitric  acid,  evaporate  in  the 
presence  of  sulphuric  acid,  and  determine  the  lead,  as  before 
stated.  Calculate  to  basic  carbonate  of  lead.  The  zinc  is 
determined  in  the  filtrate  from  the  lead  either  gravimetrically 
or  volumetrically,  as  stated  under  Zinc  Oxide.  Calculate  to  zinc 
oxide.  The  filtrate  from  the  lead  and  zinc  precipitate,  after 
removal  of  the  hydrogen  sulphide  by  boiling,  is  examined  for 
barium,  calcium,  and  magnesium,  as  stated  in  the  first  method 
for  the  analysis  of  white  pigments.  Calculate  to  carbonates. 

The  total  sulphate  present,  both  soluble  and  insoluble,  can 
best  be  determined  by  the  method  as  outlined  under  the  analysis 
of  zinc  lead  and  leaded  zinc. 

Should  the  qualitative  examination  of  the  mixed  pigment 
show  definitely  its  composition,  recourse  can  be  had  to  such 
shortened  methods  as  given  by  Thompson.* 

"Sample  i  is  a  mixture  of  barytes,  white  lead,  and  zinc 
oxide. 

"Two  i -gram  portions  are  weighed  out.  One  is  dissolved 
in  acetic  acid  and  filtered,  the  insoluble  matter  ignited  and 
weighed  as  barytes,  the  lead  in  the  soluble  portion  precipitated 
with  bichromate  of  potash,  weighed  in  Gooch  crucible  as  chro- 
mate,  and  calculated  to  white  lead. 

"The  other  portion  is  dissolved  in  dilute  nitric  acid,  sul- 
phuric acid  added  in  excess,  evaporation  carried  to  fumes,  water 
added,  the  zinc  sulphate  solution  filtered  from  barytes  and  lead 
sulphate  and  precipitated  directly  as  carbonate,  filtered,  ignited, 
and  weighed  as  oxide. 

*  J.  Soc.  Chem.  Ind.,  June  30,  1896,  Vol.  XV,  No.  6,  pp.  433,  434- 


44  ANALYSIS    OF    PAINTS  AND    PAINTING    MATERIALS. 

"Sample  2  is  a  mixture  of  barytes  and  so-called  sublimed 
white  lead. 

"Weigh  out  three  i-gram  portions.  In  one  determine  zinc 
oxide  as  in  Case  i.  Treat  a  second  portion  with  boiling  acetic 
acid,  filter,  determine  lead  in  filtrate  and  calculate  to  lead  oxide. 
Treat  third  portion  by  boiling  with  acid  ammonium  acetate, 
filter,  ignite,  and  weigh  residue  as  barytes,  determine  total 
lead  in  filtrate,  deduct  from  it  the  lead  as  oxide,  and  calculate 
the  remainder  to  sulphate.  Sublimed  lead  contains  no  hydrate 
of  lead,  and  its  relative  whiteness  is  probably  due  to  the  oxide 
of  lead  being  combined  with  the  sulphate  as  basic  sulphate. 
Its  analysis  should  be  reported  in  terms  of  sulphate  of  lead, 
oxide  of  lead,  and  oxide  of  zinc. 

"  Sample  3  is  a  mixture  of  barytes,  sublimed  lead,  and  white 
lead. 

"  Determine  barytes,  zinc  oxide,  lead  soluble  in  acetic  acid 
and  in  ammonium  acetate,  as  in  Case  2;  also  determine  carbonic 
acid,  which  calculate  to  white  lead,  deduct  lead  in  white  lead 
from  the  lead  soluble  in  acetic  acid,  and  calculate  the  remainder 
to  lead  oxide. 

"  Sample  4  is  a  mixture  of  barytes,  white  lead,  and  carbonate 
of  lime. 

"  Determine  barytes  and  lead  soluble  in  acetic  acid  (white 
lead)  as  in  Case  i .  In  filtrate  from  lead  chromate  precipitate 
lime  as  oxalate,  weigh  as  sulphate,  and  calculate  to  carbonate. 
Chromic  acid  does  not  interfere  with  the  precipitation  of  lime 
as  oxalate  from  acetic  acid  solution. 

"Sample  5  is  a  mixture  of  barytes,  white  lead,  zinc  oxide, 
and  carbonate  of  lime. 

"Determine  barytes  and  white  lead  as  in  Case  i.  Dissolve 
another  portion  in  acetic  acid,  filter  and  pass  sulphuretted 
hydrogen  through  the  boiling  solution,  filter,  and  precipitate 
lime  in  filtrate  as  oxalate;  dissolve  mixed  sulphides  of  lead  and 
zinc  in  dilute  nitric  acid,  evaporate  to  fumes  with  sulphuric 
acid,  separate,  and  determine  zinc  oxide  as  in  Case  i. 

"Sample  6  is  a  mixture  of  barytes,  white  lead,  sublimed  lead, 
and  carbonate  of  lime. 

"  Determine  barytes,  lead  soluble  in  acetic  acid  and  in  am- 
monium acetate,  as  in  Case  2,  lime  and  zinc  oxide,  as  in  Case  5, 
and  carbonic  acid.  Calculate  lime  to  carbonate  of  lime,  deduct 


THE   ANALYSIS    OF    MIXED    PIGMENTS  AND    PAINTS.  45 

carbonic  acid  in  it  from  total  carbonic  acid,  calculate  the  re- 
mainder of  it  to  white  lead,  deduct  lead  in  white  lead  from  lead 
soluble  in  acetic  acid,  and  calculate  the  remainder  to  oxide  of 
lead. 

"  Sample  7  contains  sulphate  of  lime. 

"Analysis  of  paints  containing  sulphate  of  lime  present 
peculiar  difficulties  from  its  proneness  to  give  up  sulphuric  acid 
to  lead  oxide  or  white  lead  if  present.  Sulphate  of  lime  and 
white  lead  boiled  in  water  are  more  or  less  mutually  decomposed 
with  the  formation  of  sulphate  of  lead  and  carbonate  of  lime. 
A  method  for  the  determination  of  sulphate  of  lime  is  by  pro- 
longed washing  with  water  with  slight  suction  in  a  weighed 
Gooch  crucible.  This  is  exceedingly  tedious,  but  thoroughly 
accurate.  A  reservoir  containing  water  may  be  placed  above 
the  crucible,  and  the  water  allowed  to  drop  slowly  into  it.  This 
may  take  one  or  two  days  to  bring  the  sample  to  constant 
weight,  during  which  time  several  liters  of  water  will  have 
passed  through  the  crucible.  Another  method  for  separating 
the  sulphate  of  lime  is  by  treatment  in  a  weighed  Gooch  crucible 
with  a  mixture  of  nine  parts  of  95  per  cent,  alcohol  and  one  part 
of  glacial  acetic  acid.  Acetates  of  lead,  zinc,  and  lime  being 
soluble  in  this  mixture,  the  residue  contains  all  the  su'phate  of 
lime  and  any  sulphate  of  lead  and  barytes  which  may  be  present. 
Determine  the  lead  and  lime  as  in  sample  4,  and  calculate  to 
sulphates.  Sulphate  of  lime  should  be  fully  hydrated  in  paints. 
To  determine  this,  obtain  loss  on  ignition;  deduct  carbonic 
acid  and  water  in  other  constituents;  the  remainder  should  agree 
fairly  well  with  the  calculated  water  in  the  hydrated  sulphate 
of  lime,  if  it  is  fully  hydrated.  If,  after  washing  a  small  portion 
pf  the  sample  with  water,  the  residue  shows  no  sulphuric  acid 
soluble  in  ammonium  acetate,  the  sulphate  of  lime  may  be 
obtained  by  determining  the  sulphuric  acid  soluble  in  ammonium 
acetate  and  calculating  to  sulphate  of  lime.  The  difficulty 
is  in  determining  the  sulphate  of  lime  in  the  presence,  or  possible 
presence,  of  sulphate,  of  lead.  To  illustrate  the  analysis  of 
samples  of  white  paint  containing  sulphate  of  lime  and  the 
difficulty  attending  thereon,  we  would  mention  a  sample  con- 
taining sublimed  lead,  white  lead,  carbonate  of  lime,  and  sulphate 
of  lime.  In  such  a  sample  we  would  determine  the  lead,  lime, 
sulphuric  acid,  carbonic  acid,  loss  on  ignition,  the  portion  soluble 


46  ANALYSIS    OF    PAINTS   AND    PAINTING    MATERIALS. 

in  water,  and  the  lime  or  sulphuric  acid  in  that  portion,  cal 
culating  to  sulphate  of  lime.  Deduct  the  lime  in  the  sulphate 
of  lime  from  the  total  lime,  and  calculate  the  remainder  to 
carbonate  of  lime;  deduct  the  carbonic  acid  in  the  carbonate 
of  lime  from  the  total  carbonic  acid,  and  calculate  the  remainder 
to  white  lead;  deduct  the  sulphuric  acid  in  the  sulphate  of  lime 
from  the  total  sulphuric  acid,  and  calculate  the  remainder  to 
sulphate  of  lead.  The  lead  unaccounted  for  as  sulphate  or  white 
lead  is  present  as  oxide  of  lead.  Deduct  the  carbonic  acid  and 
water  in  the  carbonate  of  lime  and  white  lead  from  the  loss  on 
ignition,  the  remainder  being  the  water  of  hydration  of  the 
sulphate  of  lime. 

"  Sample  8  contains  as  insoluble  matter,  bary tes,  china  clay, 
and  silica. 

"  After  igniting  and  weighing  the  insoluble  matter,  carbonate 
of  soda  is  added  to  it,  and  the  mixture  fused.  The  fused  mass 
is  treated  with  water,  and  the  insoluble  portion  filtered  off  and 
washed.  This  insoluble  portion  is  dissolved  in  dilute  hydro- 
chloric acid,  and  the  barium  present  precipitated  with  sulphuric 
acid  in  excess.  The  barium  sulphate  is  filtered  out,  ignited, 
weighed,  and  if  this  weight  does  not  differ  materially — say  by 
2  per  cent. — from  the  weight  of  the  total  insoluble  matter,  the 
total  insoluble  matter  is  reported  as  barytes.  If  the  difference 
is  greater  than  this,  add  the  filtrate  from  the  barium  sulphate 
precipitate  to  the  water-soluble  portion  of  fusion.  Evaporate 
and  determine  the  silica  and  the  alumina  in  the  regular  way. 
Calculate  the  alumina  to  China  clay  on  the  arbitrary  formula 
2SiO2,  A12O3,  2H2O,  and  deduct  the  silica  in  it  from  the  -total 
silica,  reporting  the  latter  in  a  free  states  It  is  to  be  borne  in 
mind  that  china  clay  gives  a  loss  of  about  13  per  cent,  on  igni- 
tion, which  must  be  allowed  for.  China  clay  is  but  slightly  used 
in  white  paints  as  compared  with  barytes  and  silica." 

"Sample  9  contains  sulphide  of  zinc. 

"  Samples  of  this  character  are  usually  mixtures  in  varying 
proportions  of  barium  sulphate,  sulphide  of  zinc,  and  oxide  of 
zinc.  Determine  barytes  as  matter  insoluble  in  nitric  acid,  the 
total  zinc  as  in  Case  i,  and  the  zinc  soluble  in  acetic  acid,  which 
is  oxide  of  zinc.  Calculate  the  zinc  insoluble  in  acetic  acid  to 
sulphide." 

"Sample  10  contains  sulphite  of  lead. 


THE   ANALYSIS    OF    MIXED    PIGMENTS   AND    PAINTS.  47 

"This  is  of  rare  occurrence.  Sulphite  of  lead  is  insoluble 
in  ammonium  acetate,  and  may  be  filtered  out  and  weighed  as 
such.  It  is  apt  on  exposure  to  the  air  in  the  moist  state  to  be- 
come oxidized  to  sulphate  of  lead. 

"There  are  certain  arbitrary  positions  which  the  chemist 
must  take  in  reporting  analyses  of  white  paints : 

"First. — White  lead  is  not  uniformly  of  the  composition 
usually  given  as  theoretical  (2PbCO3),  (PbH2O2),  but  in  report- 
ing we  must  accept  this  as  the  basis  of  calculating  results, 
unless  it  is  demonstrated  that  the  composition  of  the  white 
lead  is  very  abnormal. 

"Second. — In  reporting  oxide  of  lead  present  this  should  not 
be  done  except  in  the  presence  of  sulphate  of  lead,  and  if  white 
lead  is  present,  then  only  where  the  oxide  is  more  than  i  per  cent. ; 
otherwise  calculate  all  the  lead  soluble  in  acetic  acid  to  white 
lead. 

"Third. — China  clay  is  to  be  calculated  to  the  arbitrary  for- 
mula given. 

"  In  outlining  the  atove  methods  we  have  in  mind  many 
samples  that  we  have  analyzed,  and  the  combinations  we  have 
chosen  are  those  we  have  actually  found  present." 

General  Methods  for  the  Analysis  of  a  Mixed  Colored  Paint.— 
Such  a  paint  may  contain  any  of  the  constituents  mentioned 
under  the  various  colored  pigments.  A  qualitative  examination 
of  the  paint  will  reveal  the  composition  of  the  color  present, 
and  the  constituents  of  such  a  color  are  then  determined  as  spe- 
cifically stated  under  the  analysis  of  that  particular  colored  pig- 
ment. The  general  analysis  of  the  pigment,  excepting  that  of 
the  coloring  portion,  is  carried  out  as  stated  under  the  analysis 
of  a  mixed  white  paint. 


CHAPTER  III. 
ANALYSIS  OF  PAINT  VEHICLES  AND  VARNISHES. 

The  can  of  paint  is  allowed  to  stand  until  the  pigment  has 
thoroughly  settled,  leaving  the  vehicle  floating  on  top.  A 
quantity  of  this  separated  vehicle  is  then  removed  from  the  can 
and  carefully  preserved  in  an  air-tight  bottle,  after  determining 
its  specific  gravity.  A  weighed  portion  of  the  vehicle  may  then 
be  placed  in  a  tared  flask  and  attached  to  a  Liebig  condenser. 
Heating  to  200°  C.  will  drive  off  the  volatile  constituents.  The 
composition  of  the  distillate  may  be  determined  by  following 
the  methods  outlined  elsewhere.  The  residue  (oil,  drier  and 
gums)  may  be  transferred  to  a  crucible  and  ignited.  The 
residue  from  the  ignition  may  then  be  weighed  and  calculated 
to  ash.  An  analysis  of  this  ash  for  lead,  manganese  and  other 
driers,  may  then  be  proceeded  with  in  the  usual  manner. 

When  a  paint  is  very  thick  and  will  not  settle  so  that  the 
analyst  cannot  secure  a  good  sample  of  the  vehicle,  a  weighed 
portion  of  the  paint  may  be  placed  in  the  thimble  of  a  Soxhlet 
extractor  and  extraction  of  the  vehicle  made  in  the  usual  manner, 
with  a  known  amount  of  solvent. 

Some  operators  prefer  to  take  a  weighed  quantity  of  the  paint, 
as  it  comes  from  the  can,  say,  100  grams,  and  place  it  in  a  copper 
flask,  mixing  it  thoroughly  therein  with  sand.  Distillation  of 
this  mass  will  drive  over  the  water  and  volatile  constituents 
which  will  separate  in  two  distinct  layers  in  the  graduate  in 
which  they  are  collected.  For  the  separation  of  very  fine  pig- 
ments, such  as  certain  colors  in  oil,  a  Gooch  crucible  *  is  useful : 
Successive  extractions  of  the  pigment  are  decanted  through  a 
carefully  prepared  Gooch  crucible,  using  a  heavy  bed  of  very 
fine  asbestos,  with  a  fairly  strong  suction. 

Water. — Leo  Nemzek  of  the  North  Dakota  Agricultural  Col- 
lege, who  has  had  a  wide  experience  in  the  analysis  of  paint, 

*  Warren  I.  Keeler,  Jour.  Indus,  and  Engineer.  Chem.,  Vol.  2,  No.  9, 
p.  388. 

48 


THE   ANALYSIS    OF    PAINT   VEHICLES  AND    VARNISHES.         49 

recommends   the   following   method   for   the   determination  of 
water  in  ready-mixed  paint: 

Weigh  out  100  grams  of  the  paint  into  a  300  c.c.  Erlenmeyer 
flask,  and  heat  gradually  after  having  added  about  75  c.c.  of 
toluol.  The  heat  should  not  exceed  105°  C.  Distil  over  about 
50  c.c.  and  read  percentage  of  water.  This  method  does  not 
take  in  the  water  which  such  pigments  as  white  lead  carbonate, 
calcium  sulphate,  etc.,  give  up  at  150°  C. 

LINSEED  OIL. 

A  good  linseed  oil  will  analyze  within  the  following  limits, 
as  the  results  of  several  samples  analyzed  by  the  authors  show: 

Specific  gravity  at  15.5°  C.,  .932  to  .935 

Acid  number,  5  to  7 

Saponification  value,  187  to  192 

Unsaponifiable  matter,  .  8  to  i .  5  % 

*  Iodine  number,  180  to  190 

The  analytical  methods  outlined  by  Walkerf  are  most 
excellent.  Close  adherence  to  these  methods  have  given 
satisfactory  results  on  a  long  series  of  tests  conducted  by  the 
authors. 

i.  Preparation  of  Sample. 

"  All  tests  are  to  be  made  on  oil  which  has  been  filtered  through 
paper  at  a  temperature  of  between  15°  and  30°  C.  immediately 
before  weighing,  with  the  exception  of  tests  No.  6,  Turbidity; 
No.  7,  Foots;  No.  9,  Moisture  and  Volatile  Matter,  and  No.  10, 
Ash.  The  sample  should  be  thoroughly  agitated  before  the 
removal  of  a  portion  for  filtration  or  analysis. 

2.  Specific  Gravity. 

"  Determine  with  a  pyknometer,  plummet,  or  hydrometer 
at  15. 5°  C. 

3.  Viscosity. 

"  Use  the  Engler-Ubbelohde  method,  making  the  determina- 
tion at  20°  C. 

*  (May  sometimes  be  as  low  as  160.) 

f  P.  H.  Walker,  Some  Technical  Methods  of  Testing  Miscellaneous 
Sup'plies,  Bulletin  No.  109,  revised,  Bureau  of  Chemistry,  U.  S.  Dept. 
of  Agriculture,  1910,  pp.  n,  12  and  13. 
4 


56  ANALYSIS    OF    PAINTS   AND    PAINTING    MATERIALS. 

4.  Flash  Point,  Open  Cup. 

"  Set  a  nickel  crucible  60  mm.  in  diameter  at  the  top,  40  mm. 
in  diameter  at  the  bottom,  and  60  mm.  in  height  in  a  hole  in  the 
middle  of  a  sheet  of  asbestos  board  200  mm.  square.  The  bottom 
of  the  crucible  should  project  about  25  mm.  through  the  asbestos. 
Support  the  asbestos  on  a  tripod  and  suspend  a  thermometer 
reading  to  400°  C.  in  degrees  in  the  center  of  the  crucible,  so  that 
the  lower  end  of  the  thermometer  is  10  mm.  from  the  bottom 
of  the  crucible.  Then  pour  in  the  oil  until  its  level  is  15  mm. 
below  the  top  of  the  crucible.  Place  a  Bunsen  burner  below 
the  crucible  and  regulate  the  size  of  flame  so  that  the  thermome- 
ter rises  9°  a  minute.  As  a  test  flame  use  an  ordinary  blowpipe 
attached  to  a  gas  tube.  The  flame  should  be  about  6  mm.  long. 
Begin  testing  when  the  temperature  of  the  oil  reaches  220°  C., 
and  test  for  every  rise  of  3°.  In  applying  the  test  move  the 
flame  slowly  across  the  entire  width  of  the  crucible  immediately 
in  front  of  the  thermometer  and  10  mm.  above  the  surface  of  the 
oil.  The  flask  point  is  the  lowest  temperature  at  which  the 
vapors  above  the  oil  flash  and  then  go  out. 

5.  Fire  Point. 

"After  noting  the  temperature  at  which  the  oil  flashes  con- 
tinue the  heating  until  the  vapors  catch  fire  and  burn  over  the 
surface  of  the  oil.  The  temperature  at  which  this  takes  place 
is  the  fire  point.  In  determining  the  flash  point  note  the 
behavior  of  the  oil.  It  should  not  foam  or  crack  on  heating. 
Foaming  and  cracking  are  frequently  caused  by  the  presence  of 
water. 

6.  Turbidity. 
"  Note  whether  the  oil  is  perfectly  clear  or  not. 

7.  Foots. 

"  Let  a  liter  of  the  oil  stand  in  a  clear  glass  bottle  for  eight 
days,  and  then  note  the  amount  of  sediment  formed.  The 
highest  grades  of  oil  show  no  turbidity  or  foots  by  this  test. 
The  claim  is  made  that  sometimes  what  would  be  called  foots 
by  the  above  method  is  due  to  the  freezing  out  of  fats  of  rather 
high  melting  point.  When  a  sufficient  amount  of  the  sample  is 
available,  heat  one  portion  to  100°  C.  and  set  it  aside  for  the 


THE   ANALYSIS    OF    PAINT    VEHICLES   AND    VARNISHES.          51 

determination  of  foots,  together  with  a  sample  just  as  it  is 
received.  Note  also  the  odor  of  the  warm  oil,  rubbing  it  on  the 
hands;  a  small  amount  of  fish  oil  may  be  detected  in  this  way. 

8.  Break. 

"  Heat  50  c.c.  of  the  oil  in  a  beaker  to  300°  C.  Note  whether 
the  oil  remains  unchanged  or  "  breaks;"  that  is,  shows  clots  of  a 
jelly-like  consistency. 

9.  Moisture  and  Volatile  Matter. 

"  Heat  about  5  grams  of  oil  in  an  oven  at  105°  for  forty-five 
minutes;  the  loss  in  weight  is  considered  as  moisture.  This  de- 
termination is  of  course  not  exact,  as  there  is  some  oxidation. 
When  a  more  accurate  determination  is  desired,  perform  the 
whole  operation  in  an  atmosphere  of  hydrogen. 

10.  Ash. 

"  Burn  about  20  grams  of  oil  in  a  porcelain  dish  and  conduct 
the  ashing  at  as  low  a  temperature  as  possible.  The  best  oil 
should  contain  only  a  trace  of  ash.  An  amount  as  large  as  0.2 
per  cent,  would  indicate  an  adulterated  or  boiled  oil.  Examine 
the  ash  for  lead,  manganese,  and  calcium. 

ii.  Drying  on  Glass. 

"  Coat  glass  plates  3  by  4  inches  with  the  oils  to  be  examined, 
expose  to  air  and  light,  and  note  when  the  film  ceases  to  be  tacky. 
A  good  oil  should  dry  to  an  elastic  coherent  film  in  three  days. 
Varying  conditions  of  light,  temperature,  and  moisture  have 
such  an  influence  on  drying  tests  that  for  comparison  of  one 
linseed  oil  with  others  all  samples  must  be  run  at  the  same  time. 

12.  Drying  on  Lead  Monoxide. 

"  Livache's  test  calls  for  precipitated  lead,  but  litharge  gives 
equally  good  results.  Spread  about  5  grams  of  litharge  over 
the  flat  bottom  of  an  aluminum  dish  2 . 5  inches  in  diameter  and 
5/8  inch  high;  weigh  the  dish  and  the  litharge;  distribute  as 
evenly  as  possible  over  the  litharge  0.5  to  0.7  gram  of  the  oil, 
weigh  exactly,  expose  to  the  air  and  light  for  ninety-six  hours, 
weigh  again,  and  calculate  the  gain  in  weight  to  percentage  based 
on  the  original  weight  of  the  oil  used. 


52  ANALYSIS    OF   PAINTS  AND    PAINTING    MATERIALS. 

13.  Acid  Number. 

"Weigh  10  grams  of  oil  in  a  200  c.c.  Erlenmeyer  flask,  add  50 
c.c.  of  neutral  alcohol,  connect  with  a  reflux  air  condenser,  and 
heat  on  a  steam  bath  for  half  an  hour.  Remove  from  the  bath, 
cool,  add  phenolphthalein,  and  titrate  the  free  acid  with  fifth- 
normal  sodium  hydroxide.  Calculate  as  the  acid  number  (milli- 
grams of  potassium  hydroxide  to  i  gram  of  oil) .  The  acid  num- 
ber varies  with  the  age  of  the  oil,  and  should  be  less  than  8, 
though  when  the  oil  is  refined  with  sulphuric  acid  it  may  show 
a  higher  acid  number.  Test  for  sulphuric  acid. 

14.  Saponification  Number. 

"  Weigh  from  2  to  3  grams  of  oil  in  a  200  c.c.  Erlenmeyer 
flask,  add  30  c.c.  of  a  half -normal  alcoholic  solution  of  potassium 
hydroxide,  connect  with  a  reflux  air  condenser,  heat  on  a  steam 
bath  for  an  hour,  then  titrate  with  half-normal  sulphuric  acid, 
using  phenolphthalein  as  indicator.  Always  run  two  blanks 
with  the  alcoholic  potash.  From  the  difference  between  the 
number  of  cubic  centimeters  of  acid  required  by  the  blanks  and 
the  determinations,  calculate  the  saponification  number  (milli- 
grams of  potassium  hydroxide  to  i  gram  of  oil) .  The  saponifica- 
tion number  should  be  about  190. 

15.  Unsaponifiable  Matter. 

"As  the  saponification  varies  somewhat  in  pure  oil,  it  is 
sometimes  advisable  to  make  a  direct  determination  of  unsaponi- 
fiable  matter.  Saponify  from  5  to  10  grams  of  oil  with  alcoholic 
potassium  hydroxide  (200  c.c.  of  a  half -normal  solution)  for  an 
hour  on  a  steam  bath,  using  a  reflux  condenser.  Then  remove 
the  condenser  and  evaporate  the  alcohol  as  completely  as  possible; 
dissolve  the  soap  in  75  c.c.  of  water,  transfer  to  a  separatory 
funnel,  cool,  shake  out  with  two  portions  of  50  c.c.  each  of 
gasoline  distilled  between  35°  and  50°  C.,  wash  the  gasoline  twice 
with  water,  evaporate  the  gasoline,  and  weigh  the  unsaponifiable 
matter,  which  in  raw  linseed  oil  should  be  below  i .  5  per  cent. ;  in 
boiled  oil  it  is  somewhat  higher,  but  should  be  below  2  . 5  per  cent. 

1 6.  Iodine  Number. 

"  Weigh  in  a  small  glass  capsule  from  0.2  to  o .  25  gram  of  oil, 
transfer  to  a  350  c.c.  bottle  having  a  well-ground  stopper; 


THE  ANALYSIS    OF    PAINT    VEHICLES  AND    VARNISHES.          53 

dissolve  the  oil  in  10  c.c.  of  chloroform  and  add  30  c.c.  of  Hanus 
solution;  let  it  stand  with  occasional  shaking  for  one  hour,  add 
20  c.c.  of  a  10  per  cent,  solution  of  potassium  iodide  and  150  c.c. 
of  water,  and  titrate  with  standard  sodium  thiosulphate,  using 
starch  as  indicator.  Blanks  must  be  run  each  time.  From 
the  difference  between  the  amounts  of  sodium  thiosulphate 
required  by  the  blanks  and  the  determination,  calculate  the 
iodine  number  (centigrams  of  iodine  to  i  gram  of  oil) .  The  iodine 
number  of  raw  linseed  oil  varies  from  175  to  193,  though  Gill 
states  that  a  pure  raw  oil  may  give  a  value  as  low  as  160.  Boiled 
oil  may  be  very  much  lower. 

"Make  the  Hanus  solution  by  dissolving  13.2  grams  of  iodine 
in  1,000  c.c.  of  glacial  acetic  acid  which  will  not  reduce  chromic 
acid,  and  adding  3  c.c.  of  bromine. 

17.  Rosin  or  Rosin  Oil  (Liebermann-Storch  Test). 

"To  20  grams  of  oil  add  50  c.c.  of  alcohol,  heat  on  a  steam 
bath  for  fifteen  minutes,  cool,  decant  the  alcohol,  evaporate  to 
dryness,  add  5  c.c.  of  acetic  anhydride,  warm,  cool,  draw  off 
the  acetic  anhydride,  and  add  a  drop  of  sulphuric  acid,  i .  53 
specific  gravity.  Rosin  or  rosin  oil  gives  a  fugitive  violet  color." 

The  hexabromide  test  is  sometimes  of  value.  The  method 
used  by  Committee  E  in  their  work  on  linseed  oil  follows  :* 

"Hexabromide  Test. — On  oil,  determining  the  melting  point 
of  the  bromide  compounds.  Method  to  be  followed:  The 
determination  should  be  made  in  glass-stoppered,  weighing 
bottles,  about  6  inches  high  and  i  inch  in  diameter,  wmPrlat 
bottom,  and  weighing  about  30  grams  each.  These  bottles 
should  be  carefully  dried  and  weighed.  Weigh  into  one  of  these 
bottles  0.3  gram  of  oil  to  be  tested;  add  25  c.c.  of  absolute  ether; 
cool  to  near  o°  C.;  add  bromine,  drop  by  drop,  until  a  con- 
siderable excess  is  shown  by  the  color  of  the  solution.  Stir 
constantly  during  this  addition,  and  add  bromine  very  slowly 
to  avoid  heating.  Place  tube  in  ice  water  for  thirty  minutes; 
then  in  centrifuge,  whirling  for  two  minutes  at  speed  of  1,200 
revolutions  per  minute.  This  throws  the  brominated  oil  to 
the  bottom  of  the  tube,  from  which  the  supernatant  liquid  can 
be  easily  and  quickly  decanted.  Add  10  c.c.  of  cold  ether; 
stir  precipitate  with  glass  rod;  allow  to  stand  in  ice  water  until 

*  Proc.  Amer.  Soc.  for  Testing  Materials,  Vol.  IX,  p.  152. 


54  ANALYSIS    OF    PAINTS   AND    PAINTING    MATERIALS. 

thoroughly  cold.  Whirl  in  centrifuge  again,  and  decant  super- 
natant liquor.  Another  washing  in  the  same  manner  will 
remove  the  excess  of  bromine  and  oil.  Allow  the  tube  and 
residue  to  stand  for  a  short  time,  until  the  ether  has  evaporated; 
dry  in  water  bath  for  thirty  minutes,  and  weigh  (Tolman's 
method)." 

Acetyl  Value. 

The  determination  of  acetyl  value  is  based  on  the  principle 
that  hydroxy  acids  on  being  heated  with  acetic  anhydride 
exchange  the  hydrogen  atom  of  their  hydroxy  group  or  groups 
for  the  radicle  of  acetic  acid.  The  procedure  is  as  follows: 

Boil  the  oil  with  an  equal  volume  of  acetic  anhydride  for 
two  hours  in  a  round-bottomed  flask  attached  to  an  inverted 
condenser,  transfer  to  a  large  beaker,  mix  with  several  hundred 
cubic  centimeters  of  water  and  boil  for  half  an  hour. 

A  slow  current  of  CO2  should  be  passed  into  the  liquid 
through  a  finely  drawn-out  tube  reaching  nearly  to  the  bottom 
of  the  beaker;  this  is  done  to  prevent  bumping.  The  mixture 
is  allowed  to  separate  into  two  layers,  the  water  is  siphoned  off 
and  the  oily  layer  again  boiled  out  until  the  last  trace  of  acetic 
acid  is  removed,  which  can  be  ascertained  by  testing  with  litmus 
paper.  The  acetylated  product  is  freed  from  water  and  finally 
filtered  through  filter-paper  in  a  drying  oven. 

*"This  operation  may  be  carried  out  quantitatively,  and  in 
that  case  the  washing  is  best  done  on  a  weighed  filter.  On 
weighing  the  acetylated  oil  or  fat,  an  increase  of  weight  would 
prove  that  assimilation  of  acetyl  groups  has  taken  place.  This 
method  may  be  found  useful  to  ascertain  preliminarily  whether 
a  notable  amount  of  hydroxylated  acids  is  present  in  the  sample 
under  examination. 

"Two  or  4  grams  of  the  acetylated  substance  are  saponified 
by  means  of  alcoholic  potash  solution,  as  in  the  determination 
of  the  saponification  value.  If  the  'distillation  process'  be 
adopted  it  is  not  necessary  to  work  with  an  accurately  measured 
quantity  of  standardized  alcoholic  potash.  In  case  the  'filtra- 
tion process'  be  used,  the  alcoholic  potash  must  be  measured 
exactly.  (It  is,  however,  advisable  to  employ  in  either  case  a 

*  Commercial  Organic  Analysis,  by  Alfred  H.  Allen,  pp.  66  and  67. 
P.  Blakiston's  Son  &  Co.,  Philadelphia,  1905. 


THE   ANALYSIS    OF    PAINT    VEHICLES  AND    VARNISHES.          55 

known  volume  of  standard  alkali,  as  one  is  then  enabled  to 
determine  the  saponification  value  of  the  acetylated  oil  or  fat.) 
Next  the  alcohol  is  evaporated  and  the  soap  dissolved  in  water. 
From  this  stage  the  determination  is  carried  out  either  by  the 
(a)  'distillation  process'  or  (b)  'filtration  process.' 

"(a)  Distillation  Process. — Add  dilute  sulphuric  acid  (1:10), 
more  than  sufficient  to  saturate  the  potash,  and  distil  as  usual 
in  Reichert's  distillation  process.  Since  several  100  c.c.  must  be 
distilled  off,  either  a  current  of  steam  is  blown  through  the  sus- 
pended fatty  acids  or  water  is  run  into  the  distilling  flask,  from 
time  to  time,  through  a  stoppered  funnel  fixed  in  the  cork,  or  any 
other  convenient  device  is  adopted.  It  will  be  found  quite  suffi- 
cient to  distil  over  500  to  700  c.c.,  as  the  last  100  c.c.  contain 
practically  no  acid.  Filter  the  distillates  to  remove  any  insoluble 
acids  carried  over  by  the  steam,  and^itrate  the  filtrates  with 
decinormal  potash,  phenolphthalein  be*  the  indicator.  Multiply 
the  number  of  cubic  centimeters  by  5.61  and  divide  the  product 
by  the  weight  of  substance  taken.  This  gives  the  acetyl  value. 

"  (b)  Filtration  Process. — Add  to  the  soap  solution  a  quantity 
of  standardized  sulphuric  acid  exactly  corresponding  to  the 
amount  of  alcoholic  potash  employed  and  warm  gently,  when 
the  fatty  acids  will  readily  collect  on  the  top  as  an  oily  layer. 
(If  the  saponification  value  has  been  determined  it  is,  of  course, 
necessary  to  take  into  account  the  volume  of  acid  used  for 
titrating  back  the  excess  of  potash.)  Filter  off  the  liberated 
fatty  acids,  wash  with  boiling  water  until  the  washings  are  no 
longer  acid,  and  titrate  the  filtrate  with  decinormal  potash, 
using  phenolphthalein  as  indicator.  The  acetyl  value  is  cal- 
culated in  the  manner  shown  above. 

"Both  methods  give  identical  results;  the  latter  will  be 
found  shorter. 

"The  acetyl  value  indicates  the  number  of  milligrams  of 
KOH  required  for  the  neutralization  of  the  acetic  acid  obtained 
on  saponifying  i  gram  of  the  acetylated  fat  or  wax." 

Maumene  Test. 

While  this  test  is  not  strictly  a  quantitative  one,  the  indica- 
tions afforded  by  it  are  of  considerable  value.  It  depends  on  the 
heat  developed  by  the  mixing  of  the  oil  with  strong  sulphuric 
acid  and  is  carried  out  as  follows : 


56  ANALYSIS    OF    PAINTS   AND    PAINTING    MATERIALS. 

A  beaker  of  about  150  c.c.  capacity  and  from  7  1/2  to  9  cm. 
deep  is  carefully  placed  into  a  larger  vessel  and  surrounded  with 
dry  felt  or  cotton  waste. 

Fifty  grams  of  the  oil  are  put  into  the  beaker  and  10  c.c.  of 
concentrated  sulphuric  acid  are  gradually  introduced  into  the 
oil  from  a  burette  and  the  mixture  stirred  until  no  further  in- 
crease in  temperature  is  recorded  by  a  thermometer  immersed 
in  it. 

The  highest  point  at  which  the  thermometer  remains  con- 
stant for  any  appreciable  time  is  observed,  and  the  difference  be- 
tween this  and  the  initial  temperature  is  the  rise  of  temperature. 

In  performing  this  test,  it  is  highly  important  that  the  oil 
and  acid  be  originally  of  the  same  temperature  and  that  the 
strength  of  the  acid  should  be  the  same  as  far  as  possible. 

As  the  rise  in  temperature  varies  with  the  strength  of  the 
acid,  to  secure  uniformity  the  results  should  be  expressed  by 
dividing  the  rise  of  temperature  with  the  oil  by  the  rise  of 
temperature  with  water  and  multiplying  by  100.  This  is  called 
the  specific  temperature  reaction. 

The  rise  of  temperature  with  water  is  determined  in  the  same 
manner  as  with  oil,  using  the  same  vessel. 

Raw  linseed  oil  gives  a  Maumene  number  about  20°  F.  in 
excess  of  that  given  by  some  boiled  linseed  oils. 

Polarimetric  Test  for  Rosin  Oil  with  Linseed  Oil. 

*"The  investigations  of  Bishop  and  Peters  on  the  opticity 
of  a  number  of  oils  show  that,  with  the  exception  of  caster  oil, 
croton  oil  and  rosin  oil,  the  only  dextrorotations  are  produced  by 
sesame  (high)  and  olive  oil  (feeble),  all  the  others,  including 
linseed  oil,  being  either  optically  inactive  or  having  a  light  levo- 
rotatory  power. 

"  ( i )  The  Polarimetric  Examination  of  Linseed  Oil  Sophisti- 
cated with  Refined  Rosin  Oil  (R.  R.  O.). — According  to  Aignan 
such  a  mixture  rotates  the  plane  of  polarization  to  the  right  by 
an  angle  perceptibly  proportional  to  the  quantity  of  rosin  oil 
which  it  contains.  If  the  rotation  observed  with  a  200  mm.  tube 
be  represented  by  a  D  and  the  weight  of  the  rosin  oil  in  100 

*The  Manufacture  of  Varnishes,  and  Kindred  Industries,  Livache 
and  Mclntosh,  Vol.  I,  D.  Van  Nostrand  Company,  New  York,  1904. 


THE   ANALYSIS    OF    PAINT   VEHICLES   AND    VARNISHES.          57 

parts  by  weight  of  the  mixture  by  h,  we  get  in  the  case  of  a  mix- 
ture of  linseed  oil  with 

1.  Refined  rosin  oil,  [a]  D+  =14/15  h. 

2.  Choice  white  rosin  oil,       [aj  D  +  =17/15  h. 

3.  Rectified  rosin  oil,  [a]  D  +  =21/15  n- 

"The  first  mixture  is  the  most  common.  In  actual  practice, 
therefore,  all  that  has  to  be  done  is  to  measure  a  D  by  the  polar- 
i meter,  and  to  estimate  h  as  refined  rosin  oil,  according  to  the 
formula  h=[aJD  15/14.  The  oils  in  question  being  dark  in 
color,  it  is  better  to  work  in  a  100  mm.  tube  and  to  calculate 

h=[a]D=i5/7. 

"  (2)  Estimation  of  Rosin  Oil  in  Paint  by  the  Polarimeter. — (A) 
A  certain  amount  of  the  paint  is  frequently  stirred  and  shaken 
up  with  ether  and  allowed  to  settle.  The  ether  containing  the 
oil  in  solution  floats  to  the  surface  and  the  polarization  tube  is 
filled  with  the  ethereal  solution.  If  no  optical  deviation  be 
produced,  there  is  no  rosin  oil  in  the  paint  tested.  On  the  other 
hand,  if  [a]D  be  the  rotation  toward  the  right  with  a  200  mm. 
tube,  according  to  Aignan's  researches  on  the  rotatory  power 
of  an  ethereal  solution  of  linseed  oil  containing  rosin  oil,  the 
proportion  of  rosin  oil  may  be  calculated  by  the  formula 

,      a[D] 

h  =  ^' 

"  (B)  A  known  weight,  p1,  of  the  ethereal  solution  is  run  into 
a  flask  and  heated  on  the  water-bath  at  100°  C.  (212°  F.)  so  as 
to  drive  off  the  ether;  the  oil  which  boils  only  at  300°  C.  (572°  F.) 
is  left  in  the  flask.  Let  its  weight  be  represented  by  p2.  The 

-P1 
proportion       100  =h1  per  cent,  of  oil  (linseed  oil  and  rosin  oil) 

P2 

contained  in  the  ethereal  solution  examined  by  the  polarimeter. 
If  h1  =h,  it  may  be  taken  for  granted  that  the  paint  contained 
linseed  oil  free  from  rosin  oil.  Generally,  h1  is  greater  than  h, 

then  — 100  will  give  the  percentage  of   rosin  oil  contained  in 
h1 

the  linseed  oil  which  was  used  to  make  the  paint." 

.The  detection  of  other  vegetable  or  animal  oil,  admixed  with 
linseed  oil,  is  not  always  an  easy  task  when  they  are  present  in 
small  percentage.  Petroleum  oil  and  rosin  oil  are  the  most 


58  ANALYSIS    OF    PAINTS   AND    PAINTING    MATERIALS. 

common  adulterants.  The  detection  and  estimation  of  the 
former  is  given  on  page  52. 

The  presence  of  rosin  oil  as  an  adulterant  may  be  detected 
by  shaking  the  oil  with  an  equal  quantity  of  acetic  anhydride. 
Acetic  anhydride  is  removed  from  the  oil  and  mixed  with  a  few 
drops  of  concentrated  sulphuric  acid.  Production  of  a  violet 
color  indicates  the  presence  of  a  rosin  oil.  Its  specific  gravity 
is  very  high  and  saponification  number  very  low. 

Lewkowitsch*  shows  the  determination  of  rosin  acids  in 
admixture  with  fatty  acids,  as  follows: 

uTwitchell's  method  is  based  on  the  property  aliphatic 
acids  possess  of  being  converted  into  their  ethylic  esters  when 
acted  upon  by  hydrochloric  acid  gas  in  their  alcoholic  solution, 
whereas  colophony  practically  undergoes  little  change  under 
the  same  treatment,  abietic  acid  separating  from  the  solution. 
The  analysis  is  carried  out  as  follows: 

"  Two  to  three  grams  of  the  mixed  fatty  and  rosin  acids  are 
weighed  off  accurately,  dissolved  in  a  flask  in  ten  times  their 
volume  of  absolute  alcohol  (90  per  cent,  alcohol  must  not  be  used, 
as  the  conversion  of  fatty  acids  into  esters  is  not  complete  in 
that  case),  and  a  current  of  dry  hydrochloric  acid  gas  passed 
through,  the  flask  being  cooled  by  immersion  in  cold  water. 
The  gas  is  rapidly  absorbed  at  first,  and  after  about  forty-five 
minutes,  when  unabsorbed  gas  is  noticed  to  escape,  the  operation 
is  finished.  To  ensure  complete  esterification  the  flask  is  allowed 
to  stand  for  an  hour,  during  which  time  the  ethylic  esters  and 
the  rosin  acids  separate  on  the  top  as  an  oily  layer.  The  con- 
tents of  the  flask  are  then  diluted  with  five  times  their  volume 
of  water,  and  boiled  until  the  aqueous  solution  has  become  clear. 
From  this  stage  the  analysis  may  be  carried  out  either  (a) 
volumetrically  or  (b)  gravimetrically. 

"  (a)  The  Volumetric  Analysis — The  contents  of  the  flask 
are  transferred  to  a  separating  funnel,  and  the  flask  rinsed  out 
several  times  with  ether.  After  vigorous  shaking  the  acid 
layer  is  run  off,  and  the  remaining  ethereal  solution,  containing 
the  ethylic  esters  and  the  rosin  acids,  washed  with  water  until 
the  last  trace  of  hydrochloric  acid  is  removed.  Fifty  c.c.  of 
alcohol  are  then  added,  and  the  solution  titrated  with  standard 

*  Chemical  Technology  and  Analysis  of  Oils,  Fats,  and  Waxes, 
by  Lewkowitsch,  Vol.  I,  p.  394.  The  Macmillan  Co.,  New  York,  1904. 


THE   ANALYSIS    OF    PAINT    VEHICLES   AND    VARNISHES.          59 

caustic  potash  or  soda,  using  phenolphthalein  as  an  indicator. 
The  rosin  acids  combine  at  once  with  the  alkali,  whereas  the 
ethylic  esters  remain  practically  unaltered.  Adopting  as  the 
combining  equivalent  for  rosin  346,  the  number  of  c.c.  of  normal 
alkali  used  multiplied  by  0.346  will  give  the  amount  of  rosin  in 
the  sample. 

"  (b)  The  Gravimetric  Method. — The  contents  of  the  flask 
are  mixed  with  a  little  petroleum  ether,  boiling  below  80°  C., 
and  transferred  to  a  separating  funnel,  the  flask  being  washed 
out  with  the  same  solvent.  The  petroleum  ether  layer  should 
measure  about  50  c.c.  After  shaking,  the  acid  solution  is  run 
off,  and  the  petroleum  ether  layer  washed  once  with  water,  and 
then  treated  in  the  funnel  with  a  solution  of  0.5  grm.  potassium 
hydroxide  and  5  c.c.  of  alcohol  in  50  c.c.  of  water.  The  ethylic 
esters  dissolved  in  the  petroleum  ether  will  then  be  found  to  float 
on  the  top,  the  rosin  acids  having  been  extracted  by  the  dilute 
alkaline  solution  to  form  rosin  soap.  The  soap  solution  is 
then  run  off,  decomposed  with  hydrochloric  acid,  and  the 
separated  rosin  acids  collected  as  such,  or  preferably  dissolved 
in  ether  and  isolated  after  evaporating  the  ether.  The  residue, 
dried  and  weighed,  gives  the  amount  of  rosin  in  the  sample." 

The  detection  of  olive  oil,  palm  oil,  cocoanut  oil,  cotton-seed 
oil,  fish  oil,  and  other  vegetable  and  animal  oils  may  be  made 
by  following  the  methods  in  "Oil  Analysis,"  by  Gill  (Lippincott 
Co.).  The  low  iodine  values  of  the  above-named  oils  as  com- 
pared to  that  of  linseed  oil  is  generally  sufficient  evidence  of 
their  presence. 

SOYA  BEAN  OIL. 

Soya  bean  oil  in  its  chemical  constants  runs  so  close  to  lin- 
seed oil  that  it  is  very  hard  to  detect.  The  same  methods  can  be 
used,  however,  as  for  the  analysis  of  linseed  oil.  When  working 
upon  mixtures  of  the  two  the  following  table  of  the  authors  will 
probably  be  valuable  in  their  identification. 


60  ANALYSIS    OF    PAINTS  AND    PAINTING    MATERIALS. 

Chemical  Characteristics  Of  Soya  Bean  Oil. 


Sample 
No. 

Specific 
gravity 

Acid 
No. 

Saponifica- 
tion  No. 

Iodine 
No. 

Per  cent, 
of  foots. 

i 

,°-9233 

1.87 

188.4 

127.8 

3.8i 

2 

0.924 

1.92 

188.3 

127.2 

3 

0.9231 

i  .  90 

187.8 

*3i>7 

4 

0.9233 

1.91 

188.4 

129.8 

5" 

I  •?  o     O 

6 

132    6 

7 

i  -?6   o 

Average 


0.9234 


i .  90 


188.2 


130-7 


It  is  evident  that  the  iodine  value  of  soya  bean  oil  is  the  only 
chemical  characteristic  that  markedly  differentiates  it  from 
linseed  oil.  Therefore,  in  the  detection  of  soya  bean  oil  and  its 
estimation,  the  iodine  values  of  several  samples  of  mixed  oils  are 
given  as  being  of  interest  in  this  connection: 

Iodine  Values  Of  Linseed  Oil  And  Mixed  Oils. 


Sample 
No. 

Straight 
linseed 

i 

25%  soya. 
75%  linseed 

50%  soya. 
50%  linseed 

75%  soya. 
25%  linseed 

i 

2 

3 

190.3 

i89.5 
188.0 

175.2 
J75-9 
!75-4 

160.  7 
161  .  7 
160.3 

140.4 
140.  8 
J39-9 

Average 

189.3 

J75-5 

160.9 

140.4 

The  authors  have  found  that  treatment  of  a  few  drops  of 
soya  bean  oil,  or  oil  containing  any  considerable  percentage  of 
soya  bean  oil,  with  one  drop  of  concentrated  sulphuric  acid  will 
produce  a  distinct  fluorescent  yellowish-green  color.  This 
color  is  entirely  different  from  that  produced  with  pure  linseed 
oil,  which  is  of  a  brownish-red  and  of  a  begonia-shaped  pattern. 
This  test  is  best  conducted  on  the  lid  of  a  porcelain  crucible. 
Subsequent  examination  under  the  microscope  is  of  value  in 


THE   ANALYSIS    OF    PAINT   VEHICLES  AND    VARNISHES.          6 1 

confirming  the  test.      The  comparatively  slow  drying  of  soya 
bean  oil  will  often  indicate  its  presence. 

CHINESE  WOOD  OIL. 

Investigations,  extending  over  several  years,  conducted  by 
Kreikenbaum,*  determined  that  Chinese  wood  oil  as  it  comes 
to  the  paint  trade  is  fairly  uniform  in  its  constants.  Kreiken- 
baum's  work  also  determined  that  the  Hanus  method  for  the 
determination  of  the  iodine  number,  although  applicable  in 
the  case  of  linseed  oil,  could  not  be  used  when  working  on 
Chinese  wood  oil,  as  it  gave  abnormally  high  results.  The 
average  constants  of  a  large  number  of  commercial  samples 
determined  by  Kreikenbaum  follow: 

Specific  gravity  .941  to  .943 

Free  acid,  4 . 4 

Saponification  number,  I9°-9 

Hubl  iodine  number,  169  to     171 

Working  with  the  Hubl  method  a  six-hour  absorption  is 
sufficient  to  get  good  accurate  results  when  determining  the 
iodine  number  of  this  oil. 

SPIRITS  OF  TURPENTINE,  PETROLEUM  AND  LIGHT  OILS. 

For  a  quick  test  to  determine  whether  a  turpentine  is  pure, 
the  chemist  may  mix  in  a  test-tube  10  c.c.  of  the  material  under 
examination  and  10  c.c.  of  aniline  oil.  If  the  turpentine  is  pure, 
the  two  materials  will  mix  without  turbidity.  If  petroleum 
products  are  present,  they  will  be  indicated  by  a  cloudiness  and 
quick  separation  in  a  distinct  layer  from  the  turpentine  and 
aniline  oil. 

The  following  methods  have  been  given  by  Walker f  for  the 
analysis  of  the  volatile  solvents  used  to  a  great  extent  in  the 
manufacture  of  paints: 

*  Adolph  Kreikenbaum.  Constants  of  Chinese  Wood  Oil,  Vol.  II, 
No.  5,  Jour.  Indus,  and  Engineer.  Chem. 

f  P.  H.  Walker.  Some  Technical  Methods  of  Testing  Miscellaneous 
Supplies,  Bull.  109,  revised,  Bureau  of  Chemistry,  U.  S.  Dept.  of 
Agriculture,  1910,  pp.  13,  14,  and  15. 


62  ANALYSIS    OF    PAINTS   AND    PAINTING    MATERIALS. 

SPIRITS  OF  TURPENTINE.* 
i.  Color. 

"The  best  quality  of  spirits  of  turpentine  should  be  water- 
white. 

2.  Specific  Gravity. 

"  Determine  the  specific  gravity  with  a  pyknometer,  plum- 
met, or  hydrometer  at  15  . 5°  C.  Pure  gum  turpentine  should  have 
a  density  between  0.862  and  0.875.  Wood  turpentine  may, 
however,  range  from  0.860  to  0.910  or  even  higher. 

3.   Distillation. 

"Connect  a  distilling  flask  of  150  c.c.  capacity  with  a  con- 
denser having  a  thermometer.  Introduce  100  c.c.  of  turpentine 
and  heat  with  a  Bunsen  burner.  The  initial  boiling  point  should 
be  about  156°  C.,  and  95  per  cent,  should  distil  over  between 
153.5°  and  165.5°  C. 

4.  Residue  on  Evaporation. 

"Evaporate  10  grams  on  the  steam-bath;  the  residue  should 
be  less  than  2  per  cent. 

5.  Refractive  Index. 

"  Determine  with  a  Zeiss  direct  reading  refractometer  at  20°  C. 
The  index  of  refraction  for  gum  turpentine  should  be  from 
i .  4690  to  i .  4740;  for  wood  turpentine,  i .  4685  to  i  .5150. 

6.  Action  of  Sulphuric  Acid  (Polymerization). 

"Measure  6  c.c.  of  turpentine  in  a  stoppered,  thin-walled 
tube  graduated  to  o.i  c.c.  (carbon  tubes).  Place  the  tube  in 
cold  water  and  pour  in  slowly  a  mixture  of  four  parts  of  strong 
sulphuric  acid  and  one  part  of  fuming  sulphuric  acid.  Add 
the  acid  slowly,  and  avoid  an  excessive  rise  in  temperature. 
Shake  the  tube  so  as  to  mix  the  turpentine  and  the  acid,  add 
finally  about  20  c.c.  of  the  acid,  stopper  the  tube,  mix  thoroughly, 
cool,  allow  to  stand  thirty  minutes,  and  note  the  volume  of  un- 
polymerized  oil  that  collects  on  top  of  the  acid  layer.  Then 

*  If  wood  turpentine  has  been  carefully  refined,  it  will  comply  with 
all  the  tests  given  for  spirits  of  turpentine,  but  it  can  almost  invariably 
be  distinguished  from  the  latter  by  its  characteristic  odor. 


THE   ANALYSIS    OF    PAINT    VEHICLES   AND    VARNISHES.          63 

let  stand  for  eighteen  hours  and  again  note  the  volume.  A 
pure  turpentine  should  show  less  than  0.3  c.c.  unpolymerized 
at  the  end  of  thirty  minutes,  and  less  than  0.5  c.c.  after  eighteen 
hours. 

"  This  method  will  indicate  gross-  adulteration,  but  will  not 
detect  admixtures  of  very  small  amounts  of  mineral  oil.  Donk 
has  perfected  a  method  which  determines  the  presence  of  as  little 
as  i  per  cent,  of  mineral  oil  in  turpentine.  This  method  is  as 
follows : 

"Sulphuric  acid  of  thirty-eight  times  the  normal  strength 
(101.5  Per  cent.)  is  prepared  by  mixing  very  strong  sulphuric 
acid  with  fuming  sulphuric  acid.  It  must  be  determined  by 
titration  that  this  reagent  is  of  the  exact  strength  required,  for 
with  37.5  times  normal  acid  (100  per  cent.)  the  turpentine  is  not 
completely  destroyed,  and  with  acid  stronger  than  101 . 5  per  cent, 
the  amount  of  mineral  oil  dissolved  becomes  excessive. 

"Place  about  25  c.c.  of  the  special  sulphuric  acid  in  a  flask 
having  a  narrow  graduated  neck  (a  Babcock  bottle  does  very 
well),  cool  in  ice- water,  add  5  c.c.  of  the  turpentine  to  be  tested 
and  cool  the  flask  again,  shaking  it  carefully  and  avoiding  any 
excessive  rise  in  temperature  by  frequent  cooling.  The  flask 
should  never  be  too  hot  to  hold  in  the  palm  of  the  hand.  Then 
place  it  in  a  bath  of  cold  water  and  heat  the  bath  at  such  a  rate 
that  in  about  five  minutes  the  temperature  will  be  65°  C.  Dur- 
ing the  heating  shake  the  bottle  about  every  fifty  seconds,  finally 
shaking  very  thoroughly  so  as  to  insure  the  contact  of  every 
particle  of  the  sample  with  the  acid.  Cool  to  room  temperature 
and  add  ordinary  strong  sulphuric  acid  in  sufficient  amount  to 
bring  the  unpolymerized  liquid  up  in  the  graduated  neck.  Let 
stand  overnight  or  whirl  in  a  centrifuge  and  read  the  volume  on 
the  neck. 

"  Pure  turpentine  should  leave  a  residue  of  not  over  0.04  c.c., 
which  is  not  limpid  and  which  has  a  refractive  index  of  not  less 
than  i .  500. 

"If  the  unpolymerized  residue  is"  0.04  c.c.  or  less,  mineral 
oil  may  be  assumed  to  be  absent.  If  the  residue  is  greater, 
calculate  from  it  the  percentage  of  mineral  oil  present.  This 
will  be,  of  course,  only  approximate,  for  there  is  some  residue 
from  pure  turpentine  and  some  mineral  oil  is  dissolved  by  the 
acid;  but  for  all  practical  purposes  it  may  be  assumed  that 


64  ANALYSIS    OF    PAINTS  AND    PAINTING    MATERIALS. 

the  errors  balance  one  another,  and  hence  it  is  not  advisable  to 
apply  any  correction. 

7.  Spot  Test. 

"Place  a  drop  on  filter-paper  and  allow  it  to  dry  at  room 
temperature;  it  should  leave  no  stain. 

8.  Flash  Point. 

"  Support  a  crucible,  such  as  is  used  in  determining  the  flash 
point  of  linseed  oil,  in  a  vessel  of  water  at  15°  to  20°  C.;  the 
water  should  cover  about  two-thirds  of  the  crucible.  Fill  the 
crucible  to  within  about  2  cm.  of  the  top  with  turpentine,  insert 
a  thermometer,  and  heat  the  water  bath  slowly,  i°  per  minute. 
Begin  at  37°  and  test  for  the  flash  at  each  rise  of  0.5°.  The 
turpentine  should  not  flash  under  40.5°  C. 

Wood  Turpentine. 

The  steam  method*  for  the  distillation  of  wood  turpentine, 
as  worked  up  by  Geer,  Bristol,  Hawley,  and  others  of  the  Forest 
Products  Laboratory  of  the  United  States,  separates  the  various 
high  and  low  boiling-point  fractions,  all  of  which  have  different 
characteristics. 

BENZINE  AND  LIGHT  PETROLEUM  OILS. 

"The  term  benzine  is  used  for  a  number  of  light  petroleum 
oils.  In  the  painting  trade  it  generally  refers  to  a  product  of 
about  62°  Baume  (0.7292  sp.  gr.).  The  petroleum  benzine 
of  the  U.  S.  Pharmacopoeia  is  a  lighter  oil,  being  a  light  gasoline. 

i.  Specific  Gravity. 

"  Determine  with  a  spindle,  pyknometer,  or  plummet  at 
15.5°  C.  The  determination  can  be  made  at  room  temperature 
and  corrected  to  15.5°  C. 

2.  Sulphur  (Sodium  Nitroprusside  Test). 

"To  100  c.c.  of  the  sample  in  a  flask  add  about  i  gram  of 
bright  metallic  sodium,  connect  with  a  reflux  condenser,  and 
boil  for  one  hour.  Cool,  add  water  drop  by  drop  until  the  metal 

*  The  Analysis  of  Turpentine  by  Fractional  Distillation  with  Steam , 
by  Wm.  C.  Geer,  U.  S.  Dept.  of  Agriculture,  Forest  Service  Circular 


THE   ANALYSIS    OF    PAINT    VEHICLES  AND    VARNISHES.          65 

is  dissolved,  separate  the  aqueous  liquid,  and  test  with  a  drop  of 
sodium  nitroprusside  solution.  A  fine  violet-blue  coloration 
indicates  sulphur. 

3.  Sulphur  Compounds  and  Pyrogenous  Products  (U.  S.  P.  Test). 

"To  100  c.c.  of  the  sample  add  25  c.c.  of  a  solution  of  10  per 
cent,  anhydrous  ammonia  in  95  per  cent,  alcohol  (spirit  of  am- 
monia U.  S.  P.),  add  i  c.c.  of  silver  nitrate  solution.  Boil 
gently  for  five  minutes.  A  brown  coloration  indicates  sulphur 
compounds  or  pyrogenous  products. 

4.  Residue  on  Evaporation. 

"Place  25  c.c.  in  a  100  c.c.  platinum  dish,  heat  on  steam-bath 
for  thirty  minutes,  and  weigh  residue.  No  residue  should  be 
left  by  this  test. 

5.  Fractional  Distillation. 

"Light  petroleum  oils  are  usually  tested  only  for  specific 
gravity;  but  as  light  and  heavy  distillates  may  be  mixed,  the 
specifications  would  be  improved  by  requiring  that  a  certain 
fraction  should  distil  between  specified  temperatures.  To 
make  this  determination  distil  100  c.c.  in  a  round-bottom  flask 
6.5  cm.  in  diameter;  the  neck  should  be  1.6  cm.  in  diameter 
and  15  cm.  long,  with  a  side  tube  set  in  the  middle  of  the  neck 
at  an  angle  of  75°.  The  surface  of  the  liquid  should  be  9  cm. 
below  the  side  tube,  and  the  bulb  of  the  thermometer  just  below 
the  side  tube. 

6.  Benzol. 

"  Mix  the  sample  with  8  volumes  of  strong  sulphuric  acid  and 
2  volumes  of  nitric  acid;  heat  gently  for  ten  minutes,  allow  to 
cool,  and  note  odor.  The  odor  of  nitrobenzol  indicates  benzol. 

7.  Color  and  Odor. 

"Note  color  of  sample  and  odor  both  in  bulk  and  after 
rubbing  on  hands." 

ANALYSIS  OF  VARNISH  AND  JAPAN. 

An  examination  of  a  varnish  should  be  largely  of  a  physical 
nature,  the  chemist  determining  its  appearance,  odor,  body, 
clarity,  and  properties  of  the  dried  film.  The  specific  gravity, 

5 


66  ANALYSIS    OF    PAINTS   AND    PAINTING    MATERIALS. 

flash  point,  viscosity,  acid  number,  ash,  and  rosin  test,  as  well 
as  the  percentage  of  volatile  oils,  are  determined  in  the  usual 
manner,  as  outlined  for  linseed  oil  on  previous  pages.  The 
percentage  of  fixed  oils  and  gums  is  determined  by  weighing 
that  portion  left  in  the  flask  after  distillation  of  the  volatile 
constituents.  Owing  to  the  chemical  combinations  and  changes 
which  are  effected  when  various  gums  are  heated  together  in 
the  presence  of  oils,  it  is  almost  impossible  for  the  most  expert 
analyst  to  determine  the  exact  make-up  of  a  varnish.  The 
analyst,  however,  may  determine  the  total  percentage  of  gums 
and  the  percentage  total  of  oils  with  a  fair  degree  of  accuracy, 
on  an  original  sample  by  precipitation  of  the  insoluble  gums 
with  gasoline,  determining  the  soluble  gums  in  the  benzine  by 
extraction  with  chloroform  after  evaporation  of  the  gasoline 
and  oxidation  of  the  oil.  To  make  an  exact  determination  of  a 
varnish  formula,  however,  as  it  was  submitted  to  the  varnish 
maker,  is  almost  impossible. 

Oils,  Gums  and  Volatile. — In  ordinary  varnish  which  gen- 
erally contains  oil,  gums  and  volatile  solvents  like  benzine  and 
terpentine,  weigh  off  10  grams  into  a  tall  thin  beaker  of  400  c.c. 
capacity.  Next  add  a  large  amount  of  ice  cold  petroleum  ether. 
Cover  the  beaker  and  allow  to  stand  for  several  hours  when  the 
gums  will  be  found  separated  at  the  bottom  of  the  beaker. 
Repeat  the  extraction  with  cold  petroleum  ether  at  least  three 
times,  pouring  the  several  decanted  portions  into  a  large  bottle. 

After  finishing  the  extraction,  add  100  c.c.  of  ice  cold  water 
to  the  petroleum  ether  in  the  bottle  and  shake  thoroughly, 
causing  a  small  amount  of  gum  which  usually  dissolves  in  the 
ether  to  reprecipitate.  Filter  on  a  tared  filter,  previously 
moistened  with  ice  water,  and  also  transfer  to  this  filter  the  gum 
contained  in  the  beaker,  using  a  stirring  rod  and  some  petroleum 
ether  to  loosen  it  from  the  glass,  washing  finally  with  a  small 
quantity  of  ice  water.  Dry  at  100  C.  and  weigh  as  gums. 

If  the  oil  is  also  to  be  determined,  the  petroleum  ether  and 
water  can  be  separated  in  a  separatory  funnel  and  the  ether 
then  evaporated  or  distilled  off,  leaving  the  oil. 

The  sum  of  the  oil  and  gums  subtracted  from  100  gives  the 
percentage  of  volatile  thinners — benzine,  turpentine,  etc. 

Distillation  of  the  volatile  solvents  from  a  separate  portion 
of  the  varnish  may  be  used  to  determine  the  percentage  of 


THE   ANALYSIS    OF    PAINT    VEHICLES   AND    VARNISHES.          67 

turpentine  by  the  polymerization  method  previously  outlined 
in  this  chapter. 

In  spirit  varnishes,  like  shellac,  to  determine  the  gums  it  is 
only  necessary  to  weigh  off  10  grams  into  a  tared  porcelain  dish 
and  evaporate  off  the  solvent  on  the  water  bath- 

Mcllhiney's  method  for  the  analysis  of  oil  varnishes  has  been 
used  by  the  authors  with  success.  This  method  may  also  be 
used  in  the  analysis  of  japan  driers. 

Mcllhiney's  Method. — Of  the  materials  used  in  construction 
few  if  any  present  more  difficult  problems  in  their  testing  and 
analysis  than  oil  varnishes.  Any  rational  system  of  testing 
varnishes  to  determine  their  suitability  for  a  given  use  and 
their  resistance  to  the  destructive  effects  of  exposure  to  the 
elements,  will  take  account  among  other  tests  of  a  chemical 
analysis  to  determine  the  ingredients  of  the  varnish  and  the 
proportions  in  which  they  are  combined.  It  is  unfortunate  that 
there  is  not  at  the  present  time  any  method  of  analysis  which 
will  determine  with  any  reasonable  degree  of  accuracy,  the 
proportions  in  which  the  oil,  hard  gum,  and  common  rosin 
have  been  combined  to  form  the  nonvolatile  base  from  which  the 
varnish  is  produced  by  dilution  with  turpentine  or  other  volatile 
oil.  The  proportion  of  volatile  oil  in  the  varnish  may  be  deter- 
mined by  distilling  the  solvent  off  with  steam  at  a  temperature 
a  little  above  the  boiling  point  of  water  and  then  separating  the 
volatile  oil  from  the  aqueous  part  of  the  distillate  and  weighing 
or  measuring  it.  Its  further  examination  need  not  be  entered 
upon  here  since  methods  of  analysis  of  such  volatile  oils  as  are 
likely  to  be  used  as  thinnefs  for  varnish  are  now  generally 
known  and  are  described  at  length  in  such  standard  works  as 
Allen's  Commercial  Organic  Analysis,  and  the  books  on  paints 
and  varnishes  by  Toch,  Sabin,  and  Holley  and  Ladd. 

The  separation  of  the  hard  gum  from  the  oil  and  the  common 
rosin  is  the  problem  which  is  difficult;  the  hard  gum  and  the  oil 
do  not  unite  at  all,  practically,  until  the  hard  gum  has  been 
melted  and  from  15  to  25  per  cent,  of  its  weight  driven  off  as 
vapor,  the  amount  so  lost  depending  upon  the  character  of  the 
gum.  After  this  melting  the  linseed  oil  may  be  added  if  it  has 
been  previously  heated  enough  to  prevent  it  from  chilling  the 
melted  gum.  This  mixture  of  oil  and  gum  is  usually  at  this 


68  ANALYSIS    OF    PAINTS   AND    PAINTING    MATERIALS. 

stage  heated  for  a  shorter  or  longer  time  to  complete  the  com- 
bination of  the  ingredients.  The  union  of  oil  and  hard  gum 
which  has  been  effected  by  this  means  cannot  be  broken  up 
by  any  solvent,  or  perhaps  it  would  be  more  accurate  to  say 
that  after  the  combination  between  hard  gum  and  oil  has  been 
successfully  made  and  the  mixture  thinned  with  turpentine 
and  stored  for  a  few  months,  no  solvent  can  be  depended  upon 
regularly  to  effect  a  separation  of  the  two  by  its  selective  solvent 
action. 

The  process  which  is  here  described  depends  upon  the  fact 
that  although  the  union  between  oil  and  hard  gum  is  too  intimate 
to  be  broken  up  by  the  selective  solvent  action  of  any  solvent 
acting  directly  upon  the  original  mixture,  the  combination  may 
be  broken  up  and  the  oil  and  gum  brought  back  to  more  nearly 
their  original  condition  before  they  were  melted  together,  by 
submitting  the  mixture  to  the  action  of  caustic  potash  in  alcoholic 
solution  and  subsequently  acidifying  the  solution  of  potash 
salts  so  formed.  By  this  means  there  is  obtained  from  hard 
gum  varnishes  a  quantity  of  gum  insoluble  in  petrolic  ether 
very  closely  approximating  the  amount  of  hard  gum  actually 
existing  in  the  varnishes,  while  the  linseed  oil  is  represented 
by  its  fatty  acids  which  are  readily  soluble  in  this  solvent  unless 
they  have  been  oxidized,  in  which  case  some  of  the  fatty  acids 
of  the  linseed  oil  will  accompany  the  insoluble  hard  gum. 

In  carrying  out  the  method  an  opportunity  is  given  to 
determine  not  only  the  weight  of  the  oil  and  of  gum  but  also  the 
Koettstorfer  figure  and  the  percentage  of  glycerine  in  the 
mixture.  All  these  data  taken  together  give  a  basis  for  cor- 
roborating the  main  figures. 

The  process  is  carried  out  by  weighing  into  an  Erlenmeyer 
flask  2  to  10  grams  of  the  varnish,  adding  a  considerable  excess  of 
approximately  half -normal  solution  of  caustic  soda  or  caustic 
potash  in  very  strong  or  absolute  alcohol,  distilling  off  the  major 
portion  of  the  solvent  and  redissolving  in  neutral  absolute 
alcohol.  The  solution  is  then  titrated  with  a  solution  of  pure 
acetic  acid  in  absolute  alcohol,  approximately  half-normal 
strength,  to  determine  the  amount  of  the  excess  of  alkali  present. 
From  this  the  Koettstorfer  figure  is  determined  as  the  exact 
strengths  of  the  acid  and  alkali  solutions  have  been  ascertained 
independently  by  comparison  with  known  standards.  A 


THE   ANALYSIS    OF    PAINT    VEHICLES   AND    VARNISHES.          69 

further  quantity  of  the  standard  solution  of  acid  in  alcohol  is 
added  so  as  to  exactly  neutralize  the  total  amount  of  alkali 
originally  added.  By  this  means  the  acid  bodies  liberated 
from  their  combinations  with  alkali  are  obtained  in  solution  in 
strong  alcohol.  To  this  solution  there  is  now  added  a  sufficient 
quantity  of  petrolic  ether  to  dissolve  the  oil  acids__an 
petrolic  ether  being  miscible  with  the  strong  alcohol  forms 
with  it  a  homogeneous  liquid.  Water  is  now  added  to  the 
mixture  in  such  amount  as  to  so  dilute  the  alcohol  contained 
that  it  is  no  longer  a  solvent  for  fatty  or  resin  acids;  this  addition 
of  water  causes  the  petrolic  ether  which  was  mixed  with  the 
alcoholic  liquid  to  separate  carrying  with  it  the  fatty  acids. 
The  rosin  goes  with  the  fatty  acids  while  the  hard  gum  being 
insoluble  in  either  the  petrolic  ether  or  in  the  very  dilute  alcohol 
separates  in  the  solid  state.  The  aqueous  and  ethereal  layers 
are  now  separated  in  a  separating  funnel  and  each  is  washed, 
the  watery  layer  with  petrolic  ether  and  the  petrolic  ether  layer 
with  water.  The  petrolic  ether  layer  is  now  transferred  to  a 
weighed  flask,  the  solvent  distilled  off,  and  the  residue  of  fatty 
acids  and  common  rosin  weighed.  This  latter  is  then  examined 
further  by  Twitchell's  method  to  determine  the  amount  of  rosin 
which  it  contains  or  it  may  be  examined  qualitatively  in  a 
number  of  ways  to  establish  its  identity. 

The  aqueous  layer  is  freed  from  the  suspended  hard  gum 
which  it  contains  by  filtering,  and  from  any  further  quantity 
of  gum  which  the  weak  alcohol  may  have  retained  in  solution  by 
evaporating  off  the  alcohol  and  again  filtering.  The  remaining 
aqueous  liquid  contains  the  glycerin  and  this  is  determined  by  the 
Hehner  method  with  potassium  bichromate — the  method  ordi- 
narily used  for  examining  spent  soap  lyes. 

The  hard  gum  is,  according  to  this  plan,  precipitated  in  such  a 
way  that  it  adheres  to  the  sides  of  the  glass  vessel  in  which  the 
alcohol  and  petrolic  ether  mixture  is  diluted  with  water;  the 
easiest  method  to  weigh  it  is,  therefore,  to  carry  on  the  operation 
of  dilution  in  a  weighed  glass  vessel  and  then  to  dry  and  weigh 
the  hard  gum  in  this  vessel.  It  frequently  happens  that  some 
of  the  hard  gum  cannot  be  conveniently  retained  in  this  vessel 
but  that  it  must  be  filtered  out  on  a  weighed  filter  and  the 
weight  so  found  added  to  that  of  the  main  portion. 

If    the    varnish   contains    nonvolatile    petroleum   or   other 


70  ANALYSIS    OF    PAINTS   AND    PAINTING    MATERIALS. 

unsaponifiable  matter  it  will  naturally  be  included  in  the  fatty 
and  resin  acids,  and  it  would  be  necessary  to  saponify  the  latter 
and  extract  the  unsaponifiable  matter  from  them  while  in  the 
alkaline  state;  this  operation  is  so  familiar  to  chemists  that  it  is 
mentioned  here  only  to  call  attention  to  the  necessity  for  it  in 
some  cases. 

It  would  naturally  be  expected  that  on  account  of  the  well 
known  insolubility  of  the  oxidized  fatty  acids  in  petrolic  ether, 
some  of  the  acids  of  the  linseed  oil  which  had  been  polymerized 
by  heat  during  the  cooking  of  the  varnish,  or  which  had  been 
oxidized  during  the  blowing  process  to  which  some  linseed  oil  is 
subjected  before  making  it  up  into  varnish,  would  fail  to  dissolve 
and  would  be  counted  in  with  the  hard  gum  instead  of  with  the 
linseed  oil.  It  appears  as  a  matter  of  fact  that  this  source  of 
error  is  of  slight  importance  in  the  case  of  oil  thickened  by  heat 
but  that  the  blowing  process  gives  an  oil  which  is  not  com- 
pletely accounted  for  by  the  soluble  fatty  acids  recovered. 
This  difficulty  may  be  largely  overcome  by  taking  advantage 
of  the  greater  solubility  of  the  oxidized  fatty  acids  in  alcohol 
as  compared  with  the  hard  gum;  the  freshly  precipitated  gum 
contaminated  with  oxidized  fatty  acids  is  treated  with  a  moder- 
ate quantity  of  cold  alcohol  of  about  85  per  cent,  and  allowed 
to  digest  for  some  time.  The  soluble  matter  so  extracted  is 
then  recovered  separately  by  evaporating  off  the  alcohol. 

The  great  variety  of  hard  gums  in  use  and  in  the  methods  of 
making  them  up  into  varnish  make  the  problem  one  of  great 
complexity.  It  is  not  to  be  expected  that  any  one  method  of 
analysis  or  any  single  set  of  directions  for  carrying  on  the 
operation  of  making  the  analysis  would  be  generally  applicable, 
and  it  is  not  the  intention  in  this  paper  to  give  such  detailed 
instructions.  The  method  described  has,  however,  been  found 
to  give,  upon  samples  of  known  composition  made  up  under 
conditions  which  imitate  closely  the  conditions  of  practice  in  an 
ordinary  varnish  factory,  results  that  were  accurate  to  within 
reasonable  limits. 

Rosin  when  present  is  usually  combined  with  lime  in  the 
proportion  of  about  one  part  of  lime  to  twenty  parts  of  rosin. 
An  examination  of  the  mineral  constituents  of  the  varnish  is 
therefore  of  some  value;  the  extraction  of  the  mineral  bases 
may  be  effected  by  treating  a  quantity  of  the  varnish  somewhat 


THE   ANALYSIS    OF    PAINT    VEHICLES  AND    VARNISHES.          71 

thinned    with    benzine,    with    strong    hydrochloric    acid,    and 
examining  the  aqueous  liquid. 

The  amount  of  fatty  acids  obtained  represents  about  92 . 5 
per  cent,  of  the  linseed  oil.  The  identification  of  these  fatty 
acids  as  belonging  to  linseed  oil  or  to  china  wood  oil  may  be 
satisfactorily  accomplished  in  some  cases,  but  there  are  undoubt^ 
edly  many  varnishes  in  which  the  analyst  will  be  unable*  to 
identify  and  determine  the  oils.  The  identification  of  the  hard 
gums  after  separation  from  the  other  constituents  of  the  varnish 
is  a  matter  for  which  no  rule  can  be  given.  The  odor  and 
physical  characteristics  of  the  recovered  gum  are  quite  as 
important  as  the  known  chemical  tests  of  which  the  acidity 
and  the  Koettstorfer  figure  are  among  the  most  important. 
The  chemistry  of  these  gums  is  as  yet  almost  unknown,  but  in  the 
near  future  it  is  likely  that  our  knowledge  both  of  the  nature  of 
these  hard  gums  and  of  methods  for  separating  them  from  the 
other  ingredients  of  the  varnishes  of  which  they  form  a  part, 
will  be  very  greatly  increased. 

For  the  analysis  of  gums,  the  analyst  is  referred  to  Vols.  I 
and  II  of  Lewkowitsch,  and  to  Allen's  Commercial  Organic 
Chemistry.  The  following  method  of  Mcllhiney's  for  the 
analysis  of  shellac,  being  of  such  great  value,  is  presented  at  this 
place : 

THE  ANALYSIS  OF  SHELLAC. 

Mcllhiney's  Method.* — In  the  last  few  years  the  analytical 
examination  of  shellac  has  become  much  more  common  because 
the  users  of  shellac  and  the  dealers  in  it  have  become  better 
informed  as  to  the  extent  to  which  adulteration  has  been  prac- 
tised, in  the  past,  and  particularly  because  more  accurate  and 
reliable  methods  of  analysis  have  been  devised  for  examining 
shellac.  The  most  important  adulterant  of  shellac,  in  fact 
almost  the  only  adulterant,  is  common  rosin  or  colophony,  and 
it  is  to  the  detection  and  estimation  of  this  adulterant  that  most 
of  the  analytical  methods  have  been  directed.  The  price  of 
commercial  shellac  is  determined  by  its  color,  freedom  from  dirt, 
etc.,  as  well  as  by  its  content  of  colophony,  but  the  chemist 
is  not  usually  called  upon  to  determine  the  commercial  grade 

*  Presented  before  the  International  Congress  of  Applied  Chemistry. 


72  ANALYSIS    OF    PAINTS  AND    PAINTING    MATERIALS. 

of  shellac  in  other  respects  than  its  purity  or  freedom  from 
adulteration. 

The  methods  which  have  been  used  with  greater  or  less  suc- 
cess to  determine  the  amount  of  rosin  in  shellac  depend  first 
upon  the  different  behavior  of  shellac  and  of  colophony  toward 
alkali;  shellac  when  dissolved  in  alcohol  is  capable  of  neutralizing 
a  much  smaller  amount  of  caustic  soda  or  potash  than  rosin  when 
under  similar  conditions,  and  tests  based  upon  this  property  are 
used  and  are  of  some  value  particularly  as  corroborating  the 
results  of  other  tests.  The  difference,  however,  between  shellac 
and  rosin  in  this  respect  is  not  sufficiently  marked  nor  are  the 
various  grades  of  pure  shellac  or  of  rosin  sufficiently  constant 
in  their  behavior  when  tested  by  such  methods  to  furnish  a 
fairly  satisfactory  method  of  analysis.  (See  Allen,  Commercial 
Organic  Analysis,  Vol.  II,  Part  3,  pp.  190-195.) 

Another  property  of  rosin  which  has  been  used  to  distinguish 
and  determine  it  in  admixture  with  shellac  is  the  solubility  in 
ether  of  its  compound  or  salt  of  rosin  with  silver  while  the  similar 
compound  of  silver  with  shellac  acids  remain  undissolved.  The 
neutral  constituents  of  shellac,  that  is,  those  which  generally 
unite  with  either  soda  or  silver  are,  however,  also  soluble  in  ether 
and  are  likely  to  be  obtained  in  admixture  with  the  rosin  so 
that  this  method  of  analysis  is  objectionable. 

Shellac  and  rosin  when  treated  with  proper  solutions  of  iodine 
behave  very  differently;  the  shellac  absorbs  a  relatively  small 
amount,  varying  from  7  to  18  per  cent,  of  its  weight  of  iodine, 
the  amount  depending  upon  the  details  of  the  process  used,  while 
rosin  under  similar  conditions  absorbs  from  120  to  230  per  cent, 
of  its  weight  of  iodine.  For  many  years  it  was  the  practice  to 
use  for  the  examination  of  shellac  in  this  way  the  Hubl  process 
in  which  the  iodine  and  the  rosin  to  be  tested  are  used  in  solution 
in  alcohol  to  which  a  little  chloroform  has  been  added.  This 
Hubl  process  was  originally  designed  for  the  examination  of 
fats  and  oils  and  although  it  was  in  its  day  a  very  useful  process 
it  has  in  recent  years  been  replaced  by  others  which  are  more 
rapid  and  accurate. 

The  process  which  has  been  for  the  past  few  years  in  most 
common  use  in  the  United  States  for  the  determination  of  rosin 
in  shellac  is  the  iodine  process  which  was  originally  suggested 
for  use  upon  fats  and  oils  by  Wijs  and  which  was  later  studied 


THE   ANALYSIS    OF    PAINT   VEHICLES  AND    VARNISHES.          73 

and  adapted  for  use  upon  shellac  by  Langmuir  and  was  finally 
recommended  by  the  Sub-committee  on  Shellac  Analysis  of  the 
American  Chemical  Society  in  Journal  of  American  Chemical 
Society,  XXIX,  1221  to  1227,  as  the  most  reliable  of  those  in  use 
up  to  that  time.  The  process  consists  in  brief  of  the  following 
steps:  in  a  treatment  of  a  fixed  amount,  200  milligrams  of  the 
shellac  to  be  tested  dissolved  in  20  c.c.  of  acetic  acid  of  99  per 
cent,  strength  to  which  10  c.c.  of  chloroform  is  added,  with  20 
c.c.  of  a  solution  of  iodine  monochloride  in  acetic  acid  of  99  per 
cent,  strength  for  exactly  one  hour  at  a  temperature  of  21  to 
24°  C.  The  amount  of  iodine  which  is  absorbed  under  these 
conditions  by  rosin  is  assumed  to  be  228  per  cent,  of  the  weight 
of  the  rosin  while  shellac  absorbs  less  than  18  per  cent,  of  its 
weight  and  in  making  the  calculation  the  iodine  figure  of  the 
shellac  is  assumed  to  be  18.  This  process  has  given  excellent 
results  in  practice  particularly  as  it  is  capable  of  giving  in  the 
hands  of  different  operators  closely  agreeing  results  upon  the 
same  sample.  The  objections  to  the  use  of  this  process  are 
first  that  it  is  likely  to  give  results  below  the  truth  and  second 
that  the  method  of  ascertaining  the  amounts  of  rosin  is  an  indirect 
one  and  any  other  substance  having  a  high  iodine  figure  would  be 
counted  as  rosin;  the  rosin  itself  is  at  no  stage  of  the  process  sepa- 
rated from  the  shellac  and  submitted  to  a  separate  examination. 
The  need  of  a  process  of  analysis  which  would  actually 
separate  the  rosin  from  the  shellac  so  that  it  can  be  examined 
by  itself  has  led  the  writer  to  devise  a  process  which  has  recently 
begun  to  be  used  in  which  the  rosin  is  so  separated  from  the 
shellac.  This  process  which  was  described  at  length  in  the 
"  Journal  American  Chemical  Society, "  XXX,  867  to  872,  depends 
upon  the  fact  that  rosin  is  soluble  in  petrolic  ether  while  shellac 
is  not.  Although  it  is  not  practicable  to  extract  the  rosin  from 
solid  shellac  with  petrolic  ether,  the  latter  may  be  used  to  separate 
the  two  resins  when  they  are  dissolved  in  a  suitable  solvent.  The 
shellac  to  be  examined  is  in  this  process  dissolved  in  absolute 
alcohol  or  in  glacial  acetic  acid;  with  both  of  these  solvents 
petrolic  ether  is  miscible.  It  is,  therefore,  added  to  the  solution 
of  the  rosin,  and  to  the  resulting  mixture  water  is  added.  This 
results  in  a  separation  of  the  alcoholic  and  petrolic  ether  layers 
as  the  diluted  alcohol  is  no  longer  miscible  with  the  petrolic 
ether.  The  petrolic  ether  carries  with  it  the  rosin,  the  wax 


74  ANALYSIS    OF    PAINTS   AND    PAINTING    MATERIALS. 

contained  in  the  shellac,  providing  sufficient  petrolic  ether  was 
used  to  dissolve  it,  and  traces  of  shellac  or  of  some  constituent 
of  shellac.  Several  methods  of  separating  the  shellac  wax  from 
the  rosin  may  be  used,  but  the  most  convenient  is  to  extract  the 
petrolic  ether  solution  of  the  two  with  an  alkaline  solution  which 
removes  the  rosin  and  leaves  the  wax  dissolved  in  the  petrolic 
ether.  From  the  alkaline  solution  of  the  rosin  the  latter  may  be 
recovered  by  acidifying,  extracting  the  acidified  solution  with  a 
solvent  such  as  ether  and  distilling  of!  the  ether  to  obtain  the 
rosin  which  may  then  be  weighed. 

After  considerable  experience  with  this  method  the  following , 
details  as  to  mode  of  procedure  hav^e  been  found  convenient  as 
well  as  tending  to  give  accurate  results.  Place  2  grams  of  the 
shellac  to  be  examined  in  a  i6-oz.  flask  and  add  to  it  20  c.c. 
of  absolute  alcohol;  dissolve  the  shellac  in  the  alcohol  by  gentle 
heating.  Now  add  slowly  and  with  constant  agitation  100  c.c. 
petrolic  ether  boiling  below  80°  C.  The  first  addition  of  petrolic 
ether  to  the  alcoholic  solution  does  not  occasion  the  precipitation 
of  any  shellac,  but  as  further  quantities  are  added  the  mixed 
solvent  of  alcohol  and  petrolic  ether  becomes  incapable  of 
retaining  the  whole  of  the  shellac  in  solution  and  it  gradually 
precipitates  out.  It  is  necessary  that  the  addition  of  the 
petrolic  ether  should  therefore  be  made  slowly  and  with  stirring 
in  order  that  the  precipitating  shellac  may  not  carry  out  with  it 
mechanically  any  of  the  rosin  contained  in  the  solution.  When 
the  whole  of  the  100  c.c.  of  petrolic  ether  has  been  added  100  c.c. 
of  water  is  added  also  with  agitation.  The  first  additions  of 
water  cause  the  separation  of  the  liquid  into  two  layers  one  of 
which  is  rather  strong  alcohol,  which  may  dissolve  some  part  of 
the  rosin  which  is  afterward  precipitated  by  the  rest  of  the 
water.  The  necessity  for  agitation  during  this  stage  is  to  insure 
the  collection  into  the  petrolic  ether  of  all  the  rosin.  When 
all  the  water  has  been  added  the  liquid  is  poured  into  a  tapped 
separator  and  the  flask  rinsed  out  with  a  little  more  petrolic 
ether.  The  two  liquids  in  the  separator  readily  separate  and 
the  watery  layer  is  drawn  off.  The  petrolic  ether  is  then  washed 
with  a  little  water  which  is  also  drawn  off.  The  petrolic  ether 
is  then  filtered  into  a  clean  separator  and  to  it  is  added  25  c.c. 
of  a  solution  of  N/5  caustic  soda  in  50  per  cent,  alcohol.  This 
caustic  soda  solution  is  measured  into  the  separator  accurately 


THE   ANALYSIS    OF    PAINT    VEHICLES   AND    VARNISHES.          75 

with  a  pipette  and  a  similar  pipette  full  of  the  same  solution  is 
titrated  with  standard  hydrochloric  acid,  using  methyl  orange 
as  an  indicator.  The  separator  containing  the  alcoholic  soda 
solution  and  the  petrolic  ether  is  then  thoroughly  agitated, 
allowed  to  settle,  and  the  watery  layer  drawn  off  into  a  tared  flat, 
bottomed  dish.  The  petrolic  ether  is  then  washed  by  agitating 
with  a  little  50  per  cent,  alcohol  and  the  washings  are  added 
to  the  tared  dish.  There  is  further  added  to  the  contents  of  the 
tared  dish  the  same  volume  of  the  same  standard  hydrochloric 
acid  as  were  required  by  the  check  portion  of  25  c.c.  of  the  N/5 
soda.  J.TL  this  way  the  entire  quantity  of  soda  is  neutralized 
with  hydrochloric  acid  and  the  resinous  matters  contained  in  the 
solution  are  left  uncombined.  The  contents  of  the  dish  are  then 
allowed  to  evaporate  at  a  low  temperature  until  the  residue  is 
dry,  when  the  dish  with  its  contents  is  weighed.  The  check 
portion  of  25  c.c.  of  N/5  soda  is,  after  being  neutralized  with 
standard  acid  as  described,  evaporated  in  a  similar  dish  and  in 
this  way  the  amount  of  sodium  chloride  produced  from  the 
25  c.c.  portion  is  ascertained.  By  deducting  the  weight  of 
sodium  chloride  so  found  from  the  combined  weight  of  the 
resinous  matter  and  sodium  chloride  the  weight  of  the  former  is 
ascertained.  The  dried  contents  of  the  dish  may  now  be  further 
examined.  The  odor  of  the  resin  and  its  consistency  may  be 
observed,  its  acidity  may  be  determined  by  solution  in  neutral 
alcohol  and  titration  with  N/io  alkali  or  if  it  is  desired  the 
resinous  matter  may  be  separated  from  the  sodium  chloride  by 
dissolving  it  in  ether  or  some  other  solvent. 

By  this  process  it  is  practicable  to  actually  separate,  examine, 
and  exhibit  the  rosin  which  had  been  added  to  the  shellac  as  an 
adulterant.  It  is  also  practicable  to  determine  the  amount  of 
wax  present  providing,  however,  that  a  much  larger  amount 
of  petrolic  ether  had  been  used  than  is  necessary  for  the  complete 
extraction  of  rosin  alone.  It  has  been  found  necessary  to  use 
at  least  200  c.c.  of  petrolic  ether  per  gram  of  shellac  in  order  to 
insure  the  complete  extraction  of  the  wax,  while  50  c.c.  of  petrolic 
ether  per  gram  of  shellac  appears  quite  sufficient  to  extract  any 
reasonable  amount  of  rosin. 

As  previously  stated  the  petrolic  ether  dissolves  traces  of 
pure  shellac.  It  becomes  important,  therefore,  to  know  how 
much  will  be  dissolved  from  pure  shellac  when  examined  by  the 


76 


ANALYSIS    OF    PAINTS   AND    PAINTING    MATERIALS. 


process  above  described.  A  great  many  pure  shellacs  have 
therefore  been  examined  by  this  process  and  at  the  same  time 
their  iodine  figures  have  been  ascertained  by  the  Wijs-Langmuir 
process.  The  following  figures  are  representative  of  the  results 
obtained : 


Grade 

Acidity    of    e 
Iodine      %  Extract-        matter  per 

figure       ed  matter           in  c.c.  N/io 

extracted 
2  grams 
KOH. 

Angelo-B-Pure  Button. 
Pure  T-N  

14  .  7               2.12                           1.6 
18   o                i    70                            is 

, 

Pure  T-N 

177                    I    O  ?                                  08 

Pure  T-N  

16   o                2    19                            i    6 

Pure  T-N 

ICQ                                2O3                                                       I       Z 

Pure  T-N  
Pure  orange 

17.6                1.82                            1.5 

174.                        1^8                                          12 

Sticklac  

14    7                  ^07                               2    3 

It  will  be  noted  that  there  seems  to  be  a  tendency  for  the 
higher  grades  to  give  a  larger  amount  of  rosin  soluble  in  petrolic 
ether  than  the  lower  grades.  The  amount  given  by  such  grades 
of  shellac  as  are  likely  to  be  found  adulterated  may  safely  be 
assumed  to  be  less  than  2  per  cent.  If  the  shellac  is  of  the  highest 
grades,  those  which  seldom  contain  rosin  and  which  consequently 
seldom  need  to  be  examined  by  the  analyst,  the  amount  of  soluble 
matter  may  with  safety  be  assumed  to  be  less  than  3  per  cent. 

The  rosin  which  is  to  be  determined  consists  principally  of 
acid  bodies  which  readily  unite  with  caustic  soda,  but  it  also  con- 
tains a  certain  amount  of  unsaponifiable  matter  which  is  not 
extracted  from  the  petrolic  ether  by  the  soda  solution.  The 
amount  of  rosin  which  is  finally  weighed  cannot,  therefore,  be 
greater  than  the  amount  of  free  acids  originally  contained  in  it. 
The  amount  of  unsaponifiable  matter  contained  in  the  rosin  used 
is,  therefore  a  matter  of  interest,  but  unfortunately  it  is  impossi- 
ble to  ascertain  the  exact  amount.  It  is  reasonable  to  assume, 
however,  that  not  more  than  85  per  cent,  of  the  rosin  will  be 
recovered  and  weighed  in  the  process  above  described.  This 
assumption  agrees  perfectly  with  the  experience  in  this  labora- 
tory in  working  upon  a  considerable  variety  of  rosins. 


THE  ANALYSIS    OF    PAINT    VEHICLES  AND    VARNISHES.          77 

In  calculating  the  amount  of  rosin  content  from  the  weight 
of  extracted  resinous  matter  in  this  process,  allowance  must  be 
made  for  the  small  amount  of  pure  shellac  extracted  and  also  for 
the  shortage  in  the  weight  of  rosin  as  finally  weighed  on  account 
of  the  unsaponifiable  matters  contained  in  it. 

In  making  this  calculation  the  following  formula  is  used: 

If  Y=per  cent,  rosin, 

M  =per  cent,  of  extract  of  pure  shellac, 
N  =per  cent,  of  extract  of  pure  rosin. 
A=per  cent,  of  extract  of  mixture, 


Th         V 

rhenY=    ~x~-M~ 

Here  M=2.o  or  in  the  case  of  high  grade  shellac,  3.0,  and 
N=85.o. 

IPO  (A—  2). 
ThenY=       -^- 

Shellac  varnishes  may  contain  beside  true  shellac  not  only 
rosin,  but  other  gums  and  resins  soluble  in  alcohol.  It  becomes, 
therefore,  a  matter  of  interest  to  ascertain  how  some  of  these 
other  resins  behave  when  treated  by  this  process.  Two  samples 
of  manilla,  when  treated,  using  absolute  alcohol  as  the  first 
solvent,  gave,  respectively,  41.2  and  43.3  per  cent,  of  matter 
soluble  in  petroleum  ether.  The  acidity  of  these  two  lots  of 
matter  soluble  in  petroleum  ether  was  in  the  case  of  the  first 
sample  such  that  i  c.c.  of  normal  alkali  neutralized  411.7  mg. 
and  in  the  case  of  the  second  470.7  mg.  Two  samples  of 
Kauri  gave,  respectively,  37.9  and  27.0  per  cent.  Upon 
titrating  with  standard  alkali  these  portions  soluble  in  petro- 
leum ether,  it  appeared  that  i  c.c.  of  normal  alkali  was 
capable  of  neutralizing  903.6  mg.  and  742.5  mg.,  respectively. 
Of  Sandarac,  two  samples,  when  similarly  analyzed,  gave  34.96 
and  36.19  per  cent.,  having  such  an  acidity  that  of  the  first  541.2 
mg.  would  neutralize  i  c.c.  normal  alkali,  and  of  the  second 
552.5  mg.  would  neutralize  i  c.c.  Of  Dammar,  89.9  percent. 
proved  to  be  soluble,  while  the  resin  of  Shorea  roburta,  a  sample 
of  which  was  kindly  sent  by  Mr.  W.  Risdon  Griper,  of  Calcutta, 
gave  69.5  per  cent,  of  soluble  matter. 


APPENDIX  A. 
THE  ANALYSIS  OF  BITUMINOUS  PAINTS. 

At  the  present  time  many  bitumens  and  artificial  bitumens 
are  frequently  used,  either  alone  or  in  combination,  in  the 
manufacture  of  paints,  black  varnishes,  and  japans.  The  as- 
phaltic  compounds  are  naturally  occurring  products  in  many 
cases  containing  comparatively  large  percentages  of  sulphur. 
Mineral  matter,  which  is  present  in  widely  varying  roportions, 
consists  usually  of  limestone,  clay,  or  sandstone,  containing  the 
usual  impurities  found  in  these  materials. 

Petroleum  residuum  and  coal-tar  pitch  are  sometimes  used 
alone  as  paints,  but  more  frequently  petroleum  residuum  is 
added  to  asphaltic  compounds  as  a  flux.  Free  carbon  also  finds 
application  as  a  color  agent  for  deepening  such  mixtures,  but 
experience  has  shown  that  the  percentage  of  free  carbon  should 
not  exceed  20  per  cent. 

While  a  chemical  analysis  of  such  mixtures  will  disclose  little 
concerning  their  true  value  as  paints,  nevertheless  it  is  in  many 
cases  advisable  and  necessary  that  an  examination  be  made  so 
as  to  determine  their  general  composition.  The  following 
methods  will  be  found  to  give  good  approximate  results  in  the 
examination  of  paints  made  from  asphaltic  and  bituminous 
compounds. 

Separation  and  Determination  of  Volatile  Constituents.— 
100  grams  of  the  paint,  after  being  thoroughly  mixed,  are  placed 
in  a  distilling  flask  and  the  volatile  constituents  separated  in 
the  usual  way,  as  described  on  page  66,  all  the  volatile  con- 
stituents distilling  over  up  to  180°  C.  being  carefully  collected. 
The  amount  of  distillate  thus  found  will  give  the  percentage  of 
volatile  constituents  present.  The  distillate  is  then  fractionated 
so  as  to  determine  the  percentage  of  benzol,  benzene,  turpentine, 
and  volatile  oils.  This  operation  is  carried  out  by  the  usual 
fractionation  methods,  fractions  being  weighed  and  the  percent- 
age of  each  constituent  determined.  Separation  and  estimation 

78 


ANALYSIS    OF    BITUMINOUS    PAINTS. 


79 


of  the  turpentine  in  the  distillate  is  best  done  by  the  polymer- 
ization method  described  on  page  62. 

Any  water  present  in  the  vehicle  or  in  the  asphalt  itself, 
as  so  frequently  occurs  in  asphaltic  mixtures,  will  distil  over 
at  the  above  temperature  and  will  be  found  in  the  distillate. 

It  must  also  be  understood  that  some  low-boiling  oils  which 
are  so  often  present  in  bituminous  mixtures  may  distil  over 
at  or  below  180°  C.  When  such  oils  are  present,  it  is  impossible 
to  differentiate  between  them  and  the  oils  present  in  the  vehicle. 
In  such  cases,  however,  they  may  be  assumed  to  act  in  the 
role  of  vehicle  and  may  be  reported  as  such. 

Nonvolatile  Residue. — The  residue  left  in  the  flask  after 
distillation  is  then  examined  for  bituminous  matter  (petrolene 
and  asphaltene),  nonbituminous  matter,  carbon,  sulphur,  and 
the  constituents  entering  into  the  ash. 

Petrolene  and  asphaltene  are  the  names  applied  to  the  sub- 
stances obtained  by  the  use  of  certain  solvents  on  the  natural 
and  artificial  bitumens.  The  portion  soluble  in  petroleum  spirit, 
ether,  or  acetone  is  known  as  petrolene,  while  the  portion  in- 
soluble in  petroleum  spirit  but  dissolved  by  boiling  turpentine 
and  cold  chloroform  is  known  as  asphaltene. 

The  total  bituminous  matter  is  considered  to  be  that  portion 
of  the  asphaltic  mixture  which  is  soluble  in  the  above  solvents 
or  in  carbon  bisulphide,  the  portion  insoluble  being  considered 
as  nonbituminous  matter.  Pure  asphalt,  as  used  in  the  manu- 
facture of  painting  materials,  should  be  completely  soluble 
(with  the  exception  of  4  or  5  per  cent,  which  may  be  mineral 
matter)  in  carbon  disulphide,  oil  of  turpentine,  or  chloroform. 

Nonbituminous  Matter,  Carbon,  and  Ash. — The  residue  remain- 
ing after  the  extraction  by  the  carbon  bisulphide  method  is  dried 
and  weighed.  The  loss  between  the  original  weight  of  the  non- 
volatile residue  and  the  weight  of  the  unextracted  matter,  gives 
the  percentage  of  bituminous  matter  (asphaltene  and  petrolene) 
present.  The  insoluble  residue  after  weighing  is  ignited  until 
all  the  carbon  has  been  burned  off.  The  weight  is  again  taken 
and  the  loss  reported  as  nonbituminous  matter  and  carbon.  It 
is  advisable  before  weighing  to  treat  the  ash  with  a  little  am- 
monium carbonate  to  reconvert  any  carbonates  which  may  have 
been  decomposed  by  the  heating  to  their  original  form. 

Ash.— The    constituents  of  the  ash   are  determined  in  the 


80  ANALYSIS    OF    PAINTS  AND    PAINTING    MATERIALS. 

manner  outlined  under  the  analysis  of  mixed  pigments,  or  by 
any  of  the  methods  used  in  the  analysis  of  limestones,  clays, 
or  sandstones. 

The  mineral  matter  present  quite  frequently  exists  in  com- 
bination with  the  bituminous  matter  forming  resinous-like 
compounds  which  partially  dissolve  in  the  solvents  used  for 
fractionation  of  the  nonvolatile  residue,  thus  giving  high  results 
for  the  bituminous  matter  and  low  results  for  ash.  These 
errors,  however,  serve  to  counterbalance  each  other  and  are 
frequently  so  inappreciable  that  they  may  be  neglected. 

The  correct  percentage  of  ash  should  be  determined  by  ignit- 
ing a  new  sample  of  the  nonvolatile  residue  until  all  the  carbon 
has  been  destroyed. 

Sulphur. — It  is  often  necessary  that  the  sulphur  content  of 
asphaltic  mixtures  be  determined.  This  may  be  approximately 
determined  by  following  Eschka's  method : 

Mix  intimately  i  gram  of  the  finely  ground,  nonvolatile 
residue  with  i  gram  of  calcined  magnesium  oxide  and  .5  gram 
of  mixed  sodium-potassium  carbonates,  in  a  platinum  or  porce- 
lain crucible.  After  thorough  mixing,  the  crucible  (uncovered) 
is  heated  to  a  dull  red  heat  with  an  alcohol  or  Bunsen  flame, 
in  the  latter  case  the  crucible  being  placed  in  a  hole  cut  into  an 
asbestos  board,  thus  preventing  any  sulphur  from  the  flame 
from  contaminating  the  mixture.  The  action  is  hastened  by 
frequent  stirring  of  the  mixture.  The  heating  is  continued 
until  the  contents  of  the  crucible  become  a  dull  yellow.  Cool 
the  crucible  and  mix  the  contents  intimately  with  about  i  gram 
finely  powdered  ammonium  nitrate.  Heat  until  the  ammonium 
nitrate  is  completely  decomposed.  Any  sulphites  formed  by  the 
first  treatment  are  thus  completely  converted  into  sulphates. 

The  contents  of  the  crucible,  after  cooling,  are  carefully 
transferred  to  a  beaker  and  extracted  with  hot  water.  Evapo- 
rate, wash,  acidify  with  hydrochloric  acid  and  precipitate  the 
sulphate  present  in  the  usual  way  with  barium  chloride.  Weigh 
as  barium  sulphate  and  calculate  to  free  sulphur.  It  has  been 
found  that  the  sodium  peroxide  method  is  apt  to  give  results 
which  are  low. 

The  Hempel-  Graef e  *  method  for  determining  the  percent- 

*  J.  of  Ind.  and  Eng.  Chem.,  May,  1910,  p.  187. 


ANALYSIS    OF    BITUMINOUS    PAINTS.  8 1 

age  of  sulphur  in  bitumens  or  pyro-bitumens,  consists  in  burn- 
ing a  small  quantity  of  the  material  under  examination,  in  an 
atmosphere  of  oxygen,  with  absorption  of  the  gas  in  sodium 
peroxide.  Subsequent  neutralization  and  precipitation  is  made. 
In  determining  the  presence  and  identification  of  vegetable 
or  fossil  gums,  such  as  rosin  or  kauri  gums,  the  methods  of  Mc- 
Ilhiney  for  the  analysis  of  shellac  together  with  the  methods 
given  for  the  analysis  of  varnish  will  prove  useful. 


Examination  of  the  Nonvolatile  Residue. 

A  portion  of  about  50  grams  of  the  nonvolatile  residue  is 
placed  in  an  Erlenmeyer  flask  and  shaken  with  a  considerable 
quantity  of  carbon  bisulphide.  After  sufficient  time  has  elapsed 
for  the  carbon  bisulphide  to  exert  its  solvent  power  on  the  petro- 
lene  and  asphaltene,  the  contents  of  the  flask  are  poured  upon  a 
suitable  filter.  If  pigments  are  present,  they  will  be  found  upon 
the  filter  and  may  be  examined  by  the  methods  outlined  for  the 
analysis  of  pigments  in  mixed  paints. 

If  drying  oils,  such  as  linseed  oil,  are  present  in  the  non- 
volatile residue,  they  may  be  removed  by  treating  another  por- 
tion of  the  residue  with  88°  gasolene  for  eight  or  ten  hours. 
Evaporation  of  the  filtrate  from  this  product  will  leave  the  oils 
which  may  be  present  in  a  condition  suitable  for  analysis. 
Rosin  and  resinates  are  also  extracted  by  this  treatment  and 
should  be  looked  for.  Fossil  gums,  however,  are  apt  to  be  pre- 
cipitated by  the  gasolene. 

FORREST  METHODS. 

The  Examination  of  Black  Varnishes  and  Enamels. 

The  following  method  for  the  examination  of  paints  contain- 
ing bitumens  or  pyro  bitumens  has  been  prepared  for  this  book 
by  Mr.  C.  N.  Forrest,  Chief  Chemist  of  the  New  York  Testing 
Laboratory,  where  extensive  tests  on  the  nature  of  bituminous 
materials  have  been  conducted.  These  methods  are  of  great  im- 
portance and  serve  to  give  much  new  information  regarding 
Bituminous  Paints. 
6 


82  ANALYSIS    OF    PAINTS   AND    PAINTING    MATERIALS. 

For  the  purpose  of  an  analysis,  bituminous  paints  should  be 
divided  into  three  classes,  as  follows: 

Asphaltum  varnish. 
Asphaltum  enamel. 
Coal-tar  enamel. 

Asphaltum  varnish,  as  its  name  implies,  does  not  contain  a 
pigment  but  consists  of  a  base  of  asphatum  and  other  substances, 
reduced  to  a  fluid  consistency  with  a  suitable  volatile  solvent. 

Asphaltum  enamel  consists  of  an  asphaltum  varnish  in  com- 
bination with  a  pigment,  and  may  be  either  black  or  colored. 

Coal-tar  enamel,  although  generally  considered  as  a  varnish 
or  paint,  always  contains  carbon  in  suspension  and  therefore 
should  be  classified  as  an  enamel. 

A  distinctive  feature  of  bituminous  varnishes  and  enamels 
is  that  they  dry  by  evaporation  rather  than  by  oxidation.  If  a 
drying  oil  is  present  a  certain  degree  of  hardening  of  the  film 
subsequently  occurs,  but  the  intinal  drying  of  such  varnishes 
and  enamels  depends  upon  the  spontaneous  evaparation  of  the 
volatile  thinners  present,  and  the  rapidity  of  drying  upon  the 
degree  of  volatility  of  the  volatile  solvent.  Any  linseed  or  other 
oil  present  should  be  considered  as  a  constituent  of  the  base. 

An  asphaltum  varnish  will  therefore  consist  of  a  basic  ma- 
terial dissolved  in  from  25  to  60  per  cent,  of  some  volatile  solvent, 
such  as  turpentine,  benzine,  heavy  petroleum  spirit,  or  coal-tar 
spirit.  Occasionally  carbon  disulphide  or  some  special  solvent 
may  be  employed,  but  that  would  be  unusual. 

An  asphaltum  enamel  will  contain  black  or  colored  pigments 
combined  with  a  varnish  of  essentially  the  same  nature  as  has 
just  been  described. 

A  coal-tar  enamel  will  consist  essentially  of  a  base  of  coal- 
tar  pitch  dissolved  in  benzole  or  other  coal-tar  spirit.  The  free 
carbon  present  is  very  finely  divided  and  will  remain  suspended 
for  an  indefinite  period. 

There  are  several  kinds  of  hard  asphaltum  available  for  var- 
nish-making, but  the  principal  and  most  generally  used  types 
are  mentioned  in  the  following  table,  which  also  gives  the  im- 
portant characteristics  of  the  same. 


ANALYSIS    OF    BITUMINOUS    PAINTS. 


Refined 

Gilsonite. 

Nanjak. 

Grahamite. 

Bermudez 
asphalt. 

Gil 
pitch. 

Specific  gravity  at 

77°  F  

1.049 

i  .0844 

1.171 

1-0575 

1.0703 

Color  of  powder  .... 

Brown. 

Dark 

Black. 

Black. 

Black. 

brown. 

Melting-point  

325°F. 

35°°F. 

Intumesces. 

i7o°F. 

i64°F. 

Bitumen  soluble  in 

CS2 

QO  .  0% 

QO    2  % 

04     i  % 

06   o% 

08     2% 

Mineral  matter  .... 

W     V  f" 

.  I 

y  y  .  ^    /(j 

•3 

V  T  *           /V 

5-7 

y-'  •  **  /v 
2  .O 

v         /^ 
Trace. 

Difference  

.0 

•5 

.  2 

2  .0 

1.8 

IOO  .  O 

IOO  .0 

IOO  .  0 

IOO.  O 

IOO.O 

Bitumen  soluble  in 

88°  naphtha  

15.9 

26  .  9 

•4 

69  .  I 

69.6 

This  is  per  cent,  of 

total  bitumen.  .  .  . 

15-9 

27.0 

•4 

71.9 

70.9 

Residual   coke 

1  3    4. 

2  S     O 

C-I   .  -2 

14  .  o 

10  •  "? 

Paraffine  

Ao  •  t 

None. 

*  j  •  v 

None. 

JO      0 

None. 

None. 

-1  V  •  0 

.8 

Characteristics     o  f 

asphaltenes     i  n  - 

soluble    in    88° 

naphtha. 

Color  

Black. 

Black. 

Black. 

Brown. 

Brow^n. 

Condition  

Hard. 

Hard. 

Hard. 

Soft. 

Soft. 

Residual  coke  

15-2°% 

55-6o% 

50-55% 

30-35% 

50-60% 

84 


ANALYSIS    OF    PAINTS  AND    PAINTING    MATERIALS. 


The  characteristics  of  the  most  select  grades  of  coal-tar  pitch 
suitable  for  the  manufacture  of  enamel  are  as  follows : 


Coal-tar  Pitch. 


Hard. 

1 

Soft. 

Specific  gravity  at  77°F 

I     24. 

I     2  ^ 

Color  of  powder  

Black 

Black. 

Melting-point    

i6i°F 

i4o°F 

Bitumen  soluble  in  CS2  

04  .  I  % 

92   2% 

Mineral  matter  

I 

i 

Free  carbon    etc 

^   8 

77 

Bitumen  soluble  in  88°  naphtha. . 
This  is  per  cent,  of  total  bitumen 
Residual  coke. . 


85  •  o 
9° -3 


87.0 
94.4 
25.1 


The  characteristics  of  the  most  select  grade  of  stearine  pitch, 
Calabrea  pitch,  and  of  the  resins  sometimes  included  in  black 
varnishes  are  as  follows: 


CALABRIA  PITCH. 


Specific  gravity  at  77°  F. 

Color  of  powder 

Melting-point 

Bitumen  soluble  in  CS2.  . 
Mineral  matter . . 


Bitumen  soluble  in  88°  naphtha    

This  is  per  cent,  of  total  bitumen 

Residual  coke 

Characteristics  of  asphaltenes  insoluble  in  88° 
naphtha. 


Color 

Condition .... 
Residual  coke 


1.030 
Black. 
i6i°F. 
99-5% 

•5 


IOO  .  O 

41.3 
41-5 


Black. 

Spongy — melts. 
21.8% 


ANALYSIS    OF    BITUMINOUS    PAINTS.  85 

Resins. 


Colophony. 

Kauri. 

Copal. 

Soluble  in  88°  naphtha  

1  00% 

4.    0% 

25    0% 

Residual  coke    

Trace 

Trace 

Trace 

There  is  no  established  custom  followed  in  the  selection  of 
the  other  materials  which  are  combined  witn  hard  asphaltum 
in  the  preparation  of  the  base  of  a  varnish. 

Such  materials  include  rosin,  fossil  gums,  linseed  oil,  China 
wood-oil,  mineral  oil,  driers,  and  other  substances.  The  purpose 
of  the  use  of  such  materials  is  to  modify  the  degree  of  hardness 
and  flexibility,  facilitate  the  thinning  operation  and  increase 
durability  according  to  the  service  the  finished  varnish  is  to 
perform. 

A  coal-tar  enamel  is  usually  nothing  more  than  a  coal-tar 
pitch  dissolved  in  coal-tar  spirit.  It  may  sometimes  contain 
rosin  or  a  small  amount  of  linseed  oil,  but  that  is  unusual.  It  is 
not  customary  to  mix  coal-tar  pitch  and  asphaltum  for  a  varnish 
base  as  the  two  materials  do  not  combine  readily  and,  if  com- 
bined, are  furthermore  generally  but  partially  soluble  in  petro- 
leum spirit,  the  least  costly  solvent  employed  in  this  industry. 

A  practical  test  should  always  be  made  by  applying  a  coat 
of  the  varnish  or  enamel  on  a  surface  similar  to  that  upon  which 
it  is  to  be  used  and  the  covering  or  hiding  capacity,  spreading 
qualities,  time  of  drying,  etc.,  noted.  An  outdoor  exposure  test 
on  a  small  steel  plate  of  the  materials  intended  for  such  use 
should  also  be  made. 

The  first  step  in  the  analysis  of  bituminous  varnishes  and 
enamels  should  be  to  separate  the  volatile  thinners  from  the  base, 
and  this  is  most  conveniently  done  by  distilling  about  50  grams 
in  a  flask  by  gentle  heat.  A  nonoxidizing  atmosphere  should 
be  maintained  in  the  flask  during  the  distillation  by  the  intro- 
duction of  CO,  or  other  inert  gas.  The  difference  in  the  boiling- 
point  of  the  solvent  and  the  base  is  so  great  that  a  clean  separa- 
tion may  be  readily  made  by  this  method. 

The  temperature  at  which  the  volatile  thinners  pass  over 
should  be  noted  and  a  subsequent  examination  of  the  distillate 
for  volume,  specific  gravity,  flash-point,  and  indifference  to  strong 


86  ANALYSIS    OF    PAINTS   AND    PAINTING    MATERIALS. 

sulphuric  acid  will  give  sufficient  data  for  the  identification  of 
the  same  and  the  amount  present. 

While  the  base  in  the  distilling  flask  is  still  fluid  it  should 
be  poured  into  a  shallow  tin  box.  The  portion  adhering  to  the 
flask  may  be  removed  with  carbon  disulphide,  the  solvent 
expelled,  and  the  residue  combined  with  the  chief  portion.  This 
precaution,  however,  need  not  be  observed  unless  a  pigment  is 
present. 

The  amount  of  pigment  may  be  determined  by  treating  10  to 
50  grams  of  the  base  with  100  c.c.  carbon  disulphide  in  a  small 
Erlenmeyer  flask  and  filtering  through  a  Gooch  crucible,  washing 
with  the  same  sovlent,  or  by  extracting  with  carbon  disulphide 
in  a  Soxhlet. 

Having  separated  the  pigment  as  above  and  recovered  the 
soluble  portion  by  evaporating  off  the  solvent,  the  analysis 
should  proceed  exactly  as  in  the  case  of  a  clear  asphaltum  var- 
nish base. 

From  i  to  5  grams  of  the  base,  in  a  finely  divided  condition, 
should  be  treated  in  an  Erlenmeyer  flask  with  100  to  200  c.c. 
88°  naphtha  and  allowed  to  stand  over  night  at  laboratory 
temperature.  The  naphtha  is  then  decanted  through  a  Gooch 
or  filter-paper,  the  residue  transferred  to  the  filter  and  washed 
with  the  solvent  until  the  filtrate  runs  through  clear. 

The  filtrate  will  contain  the  rosin  drying  and  petroleum  oils 
and  a  portion  of  the  asphaltum  or  pitch  if  any  is  present. 

The  insoluble  residue  will  consist  essentially  of  the  so-called 
asphaltenes  of  the  asphaltum,  and  will  generally  represent  from 
30  to  85  per  cent,  of  the  amount  of  asphaltum  in  the  base, 
depending  upon  what  variety  of  the  same  has  been  employed. 
In  the  case  of  Grahamite,  it  would  represent  practically  all  of  the 
asphaltum  present,  but  that  material  is  not  in  general  use  in 
varnishes. 

The  color  and  hardness  of  the  insoluble  residue  should  be 
noted  and  a  determination  of  residual  coke  or  fixed  carbon 
made  as  follows: 

One  gram  of  residue  is  ignited  in  a  platinum  crucible,  as  in 
the  proximate  analysis  of  coal,  Jour.  Amer.  Chem.  Soc.,  Vol.  21, 
p.  1116,  1899. 

If  the  residue  is  dark  brown  and  soft  and  has  a  fixed  carbon 
of  about  50  per  cent,  the  asphaltum  is  probably  an  oil  pitch. 


ANALYSIS    OF    BITUMINOUS    PAINTS.  87 

If  it  is  black  and  hard  and  has  a  fixed  carbon  of  about  50  per 
cent,  it  is  probably  grahamite.  If  black  and  hard  and  about 
15  per  cent,  fixed  carbon  it  is  gilsonite.  If  dark  brown  and  soft 
and  about  30  per  cent,  fixed  carbon  it  is  probably  Bermudez 
asphalt. 

The  filtrate  after  expelling  the  solvent  used  in  the  extraction 
may  be  tested  for  saponification  and  iodine  values  and  for  rosin 
by  the  Lieberman  or  Storch  test.  If  a  quantitative  separation 
of  rosin  is  desired  the  laborious  Twitchell  method  must  be  re- 
sorted to. 

The  difference  between  the  saponifiable  and  the  total  soluble 
in  88°  naphtha  will  give  the  mineral  oils  and  so-called  petrolenes 
of  the  asphaltum. 

A  positive  test  for  and  approximate  determination  of  coal-tar 
may  be  made  by  distilling  a  small  amount  of  the  base  in  a  glass 
retort  to  coke,  and  mixing  4  c.c.  of  the  distillate  thus  obtained 
with  6  c.c.  dimethyl  sulphate  in  a  graduated  tube.  Coal-tar 
distillates  are  entirely  soluble  in  dimethyl  sulphate,  while  those 
from  asphaltum,  petroleum,  and  vegetable  paint  oils  and  resins 
are  insoluble.  See  Jour.  Ind.  and  Eng.  Chem.,  Vol.  II,  p.  186, 
May,  1910. 

The  pigment  separated  from  asphaltum  enamels  may  be 
examined  in  detail  if  desired  by  the  same  methods  employed  in 
the  analysis  of  linseed  oil  and  house  paint. 

The  combinations  in  use  by  various  manufacturers  in  the 
making  of  black  varnishes  are  frequently  very  complicated. 

Baking  enamels  for  certain  specific  uses  require  speicia 
formulae,  but  for  the  general  line  of  black  varnishes  the  princpall 
object  is  to  produce  a  base  of  high  gloss  and  deep  color,  having 
some  flexibility,  which  will  reduce  with  turpentine  or  benzine 
at  a  temperature  sufficiently  low  to  avoid  excessive  loss  of 
solvent  in  the  manufacturing  process. 

To  this  end  it  is  usually  sufficient  to  fuse  an  asphaltum  of 
the  gilsonite  type  with  rosin,  linseed,  or  mineral  oil  in  sufficient 
amount  to  reduce  the  melting-point  of  the  asphaltum  without 
rendering  it  unduly  soft. 

The  durability  of  the  film  of  varnish  is  affected  by  the  fluxing 
material  used  as  well  as  its  degree  of  hardness  and  flexibility,  and 
the  desire  to  produce  a  cheap  varnish  frequently  overbalances 
the  desire  to  produce  a  durable  one. 


88  ANALYSIS    OF    PAINTS  AND    PAINTING    MATERIALS. 

The  base  of  a  varnish  for  outdoor  exposure  to  sunlight  and 
atmospheric  conditions  should  be  of  a  different  character  both 
in  degree  of  hardness  and  composition  from  varnishes  intended 
for  damp-proofing,  insulating,  and  acid,  and  alkali  resisting 
purposes. 

There  is  nothing  to  be  gained  by  the  use  of  turpentine  and 
other  expensive  solvents  instead  of  benzine  or  heavy  petroleum 
spirit,  provided  the  base  is  entirely  soluble  in  the  latter  and  a 
proper  selection  has  been  made  to  assure  the  drying  properties 
desired.  Varnish  makers'  benzine  (62°B.)  evaporates  too  fast 
to  be  satisfactory  as  the  thinning  material  of  a  heavy  brush 
varnish.  On  the  other  hand,  it  is  indispensable  in  thin  quick- 
drying  brush  varnishes  and  dips. 

On  account  of  the  extremely  complex  nature  of  black  varnish 
bases  it  is  quite  impossible  to  prescribe  a  general  method  which 
may  be  followed  without  modification  and  cover  all  features  of 
this  subject. 

The  foregoing  is,  therefore,  given  more  as  an  outline  for  the 
guidance  of  those  analysts  who  are  capable  of  adapting  the 
general  schemes  of  classification  and  separation  to  the  particular 
purpose  at  hand,  and  supplementing  the  same  with  such  further 
tests  as  will  develop  the  special  features  of  the  material  if  the 
simple  separations,  etc.,  specifically  mentioned  are  not  sufficient . 


APPENDIX  B. 

The  following  specifications  of  the  Army  and  Navy  Depart- 
ments are  given  so  that  the  chemist  engaged  in  the  examination 
of  such  materials  may  become  better  acquainted  with  the 
requirements.  These  specifications,  however,  refer  only  to  the 
chemical  requirements,  and  for  full  specifications  the  reader  is 
referred  to  the  Bureau  of  Supplies  and  Accounts  of  the  United 
States  Navy,  Washington,  D.  C. 

SPECIFICATIONS   ISSUED   BY  THE   ARMY  DEPARTMENT. 

Pure  White  Lead.— White  lead  must  be  of  the  best  quality, 
finely  ground  in  pure  well-settled  raw  linseed  oil;  must  be  of 
maximum  whiteness;  must  work  freely  under  the  brush,  and  not 
be  crystalline  in  structure  nor  deficient  in  density  and  opacity. 
Dry  pigment  must  contain  at  least  98  per  cent,  of  hydrate 
carbonate  of  lead.  Its  workings  under  the  brush,  maximum 
whiteness,  body,  and  covering  qualities  to  be  determined  by 
practical  test. 

White  Zinc. — American  Process. — The  dry  pigment  must 
contain  at  least  98  per  cent,  of  oxide  of  zinc,  not  more  than  0.5 
per  cent,  of  sulphur  in  any  form,  and  be  of  the  quality  known 
as  "XX." 

French  Process. — The  dry  pigment  must  contain  at  least 
99  per  cent,  of  oxide  of  zinc  and  not  more  than  0.25  per  cent, 
of  sulphur  in  any  form,  and  to  be  of  maximum  whiteness  as 
compared  with  standard  sample. 

Venetian  Red. — The  dry  pigment  must  contain  at  least  40 
per  cent,  of  sesquioxide  of  iron,  not  more  than  15  per  cent,  of 
silica,  the  balance  to  consist  of  sulphate  of  lime  that  has  been 
fully  dehydrated  by  dead  burning  and  rendered  incapable  of 
taking  up  water  of  crystallization. 

Indian  Red. — Must  be  of  good  rich  color.  The  dry  pigment 
must  contain  at  least  95  per  cent,  of  oxide  of  iron  (Fe2O3),  and 


QO  ANALYSIS    OF    PAINTS  AND    PAINTING    MATERIALS. 

be  free  from  sulphur  and  alkali.     Pale  shade  is  desired  in  the 
absence  of  other  specifications. 

Vermilion. — American  (dry). — Must  be  of  good,  bright  color, 
and  contain  at  least  98  per  cent,  of  basic  chromate  of  lead,  and 
be  free  from  any  foreign  coloring  matters. 

English  (dry). — Must  contain  at  least  99  per  cent,  of  red 
sulphide  of  mercury;  must  be  free  from  any  foreign  coloring 
matters  or  alkali  in  any  form. 

Artificial. — The  dry  pigment  must  be  the  lead-barium  lake 
of  the  azo  dye  known  commercially  as  "  Lithol." 

Raw  and  Burnt  Sienna. — The  dry  pigment  must  be  equal 
in  quality  to  the  best  selected  Italian  sienna,  and  must  not 
contain  more  than  5  per  cent,  of  lime  in  any  form. 

Yellow  Chromes. — Must  be  of  good  bright  color  and  full 
strength.  The  dry  pigment  must  contain  at  least  98  per  cent, 
of  normal  chromate  or  basic  chromate  of  lead. 

Yellow  Ochre. — It  must  be  equal  in  color  and  quality  to  the 
best  French  ochre  and  be  free  from  any  chromate  of  lead  or 
foreign  coloring  matter.  The  dry  pigment  must  contain  at 
least  20  per  cent,  of  oxide  of  iron  and  not  more  than  5  per  cent,  of 
lime  in  any  form. 

Chrome  Green. — Chrome  green  must  be  of  good  bright  color. 
The  dry  pigment  must  contain  25  per  cent,  chrome  green  made 
by  mixture  of  pure  chrome  yellow  and  Russian  blue  and  75  per 
cent,  barium  sulphate.  Medium  shade  is  desired  in  absence  of 
other  specifications. 

Drop  Black. — Drop  black  must  be  of  good  deep  luster  and 
consist  of  calcined  bone-black  only.  The  addition  of  blue  or  gas 
carbon-black  will  be  ground  for  rejection.  The  paste  must 
contain  not  less  than  45  per  cent,  of  pure  pigment. 

Oil  Lamp-black  for  Tinting  Purposes. — The  pigment  must  be 
the  perfectly  calcined  product  of  oils  only  and  show  less  than 
2  per  cent,  of  ash.  It  must  be  absolutely  neutral,  free  from  oil 
or  greasy  matter,  grit,  and  all  impurities.  The  pigment  reduced 
in  white  must  give  a  clear  blue-gray  tone  or  tint. 

Japan  Drier. — Japan  drier  must  not  flash  below  103°  F. 
(open  tester) ;  must  be  of  the  best  quality  and  made  from  pure 
kauri  gum,  pure  linseed  oil,  pure  turpentine  and  the  proper 
driers  only;  must  set  to  touch  in  from  one-fourth  to  one  hour, 
dry  elastic  in  from  eighteen  to  twenty-four  hours  at  a  temperature 


PAINT    SPECIFICATIONS.  9 1 

of  70°  F.,  and  must  not  rub  up  or  powder  under  friction  by  the 
ringer.  When  mixed  with  pure  raw  linseed  oil  in  the  proportion 
of  eight  parts  of  oil  to  one  part  of  drier  must  remain  clear  for  two 
hours  and  set  to  touch  in  from  six  to  seven  hours  at  a  temperature 
of  70°  F. 

Varnish. — All  varnishes  other  than  those  which  have  definite 
specifications  must  be  pure  turpentine  hard-gum  varnishes  and 
absolutely  free  from  rosin  or  any  turpentine  substitutes. 

Damar  Varnish. — It  must  be  made  from  solution  of  the  very 
best  quality  of  damar  gum;  such  solution  to  contain  at  least  50 
per  cent,  of  gum  with  45  per  cent,  turpentine.  It  must  be  digested 
cold  and  well  settled.  It  must  be  as  clear  as  and  not  darker 
than  the  standard  sample.  It  must  be  free  from  benzine,  rosin, 
and  lime  or  other  mineral  matter.  Its  specific  gravity  at  60°  F. 
must  be  between  .935  and  .937  and  its  flash  point  between  105° 
and  115°  F.  It  must  set  to  touch  in  not  more  than  twenty 
minutes,  and  when  mixed  with  pure  zinc  oxide  must  show  a 
smooth  glossy  surface  equal  to  that  shown  by  the  standard 
sample. 

Tests. — Besides  chemical  tests  to  determine  the  above  quali- 
ties and  practical  tests  to  determine  its  qualities  of  finish,  a 
board  properly  coated  with  a  mixture  of  zinc  and  the  liquid 
will  be  exposed  to  the  weather  for  a  period  of  one  month,  and  at 
the  end  of  this  time  must  have  stood  such  exposure  equally  as 
well  as  the  standard  sample.  A  similarly  prepared  sample  will 
also  be  baked  at  250°  F.,  and  must  not  at  this  temperature  show 
any  greater  signs  of  cracking,  blistering,  or  any  other  defects 
than  standard  samples  under  the  same  conditions. 

Asphaltum  Varnish. — Asphaltum  varnish  must  be  made  of 
pure  high-grade  asphaltum  of  the  very  best  quality,  of  pure 
linseed  oil  and  pure  turpentine  dryers  only,  and  must  not  con- 
tain less  than  20  gallons  of  prepared  linseed  oil  to  100  gallons 
of  varnish.  It  must  not  flash  below  103°  F.  (open  tester).  It 
must  mix  freely  with  raw  linseed  oil  in  all  proportions;  must 
be  clear  and  free  from  sediment,  resin,  and  naphtha.  When 
flowed  on  glass  and  allowed  to  drain  in  a  vertical  position  the 
film  must  be  perfectly  smooth  and  of  full  body,  and  must  equal 
in  this  last  respect  the  standard  sample.  It  must  set  to  touch 
in  from  one  and  one-half  to  two  and  one-half  hours  and  must 
dry  hard  in  less  than  twenty  hours  at  70°  F.  When  dry  and 


92  ANALYSIS    OF    PAINTS  AND   PAINTING    MATERIALS. 

hard  it  must  not  rub  up  or  powder  under  friction  by  the  finger. 
The  application  of  heat  must  quicken  the  time  of  drying  and 
give  a  harder  film. 

SPECIFICATIONS   ISSUED   BY  THE   NAVY   DEPARTMENT. 

White  Lead  in  Oil. — The  dry  pigment  must  be  of  the  best 
quality,  must  not  be  crystalline  in  structure  or  deficient  in 
density  or  opacity.  Unless  otherwise  specified,  white  lead  will 
be  delivered  in  paste  form,  the  pigment  finely  ground  in  pure 
raw  linseed  oil,  and  in  paste  form  must  not  contain  more  than 
0.5  per  cent,  of  moisture.  The  dry  pigment  must  be  a  pure 
hydrated  carbonate  of  lead,  free  from  all  adulterants,  and  equal 
in  quality  to  the  best  commercial  grades.  The  total  acetate 
must  not  be  in  excess  of  the  equivalent  of  0.15  per  cent,  of 
absolute  acetic  acid. 

Specifications  for  Whiting. — The  material  must  be  free 
from  grit;  must  contain  not  more  than  i  .5  per  cent,  of  matter 
insoluble  in  dilute  hydrochloric  acid,  and  not  more  than  4/10 
per  cent,  oxides  of  iron  and  aluminum  (determined  together). 

Specifications  for  Chrome  Green. — The  dry  pigment  must 
be  of  a  good  bright  color  and  must  contain  at  least  98  per  cent, 
by  weight  of  pure  lemon  chrome  and  Chinese  blue,  which  mix- 
ture must  not  contain  more  than  10  per  cent,  by  weight  of 
lead  sulphate  and  rnust  be  equal  in  all  respects  to  the  standard 
sample.  A  medium  shade  is  desired  in  the  absence  of  other 
specifications. 

Metallic  Brown. — i.  The  dry  pigment  must  contain  not 
less  than  45  per  cent.,  by  weight,  of  oxide  of  iron  and  must  not 
contain  more  sulphur  in  combination  than  the  equivalent  of 
2  per  cent.,  by  weight,  of  sulphur  trioxide  (SO3). 

2.  It  must  be  ground  perfectly  pure,  not  made  from  or 
adulterated  with  the  by-products  of  sulphuric  acid  works,  and 
must  be  free  from  makeweights  or  adulterants.  When  in  paste 
form,  it  must  contain  at  least  20  per  cent.,  by  weight,  of  pure 
raw  linseed  oil. 

Chinese  Blue. — i.  The  dry  pigment  must  contain  not  less 
than  98  per  cent.,  by  weight,  pure  coloring  matter  of  the  best 
quality,  free  from  adulterants,  and  equal  in  every  respect  to  the 
standard  sample. 


PAINT    SPECIFICATIONS.  93 

2.  When  in  paste  form,  the  paste  must  contain  not  less  than 
50  per  cent,  by  weight  of  pure  pigment  ground  in  absolutely 
pure,  well-settled,  and  perfectly  clear  raw  linseed  oil  of  the  best 
quality  only  to  a  medium  stiff  consistency,  which  will  break  up 
readily  in  thinning,  and  must  be  free  from  grit,  adulterants,  and 
all  impurities. 

Red  Lead,  Dry. — The  dry  pigment  must  be  of  the  best 
quality,  free  from  all  adulterants,  and  contain  at  least  94  per 
cent,  of  true  red  lead(p^) — equivalent  to  32.8  per  cent,  of 
lead  peroxide  (Pb°) — ,  the  balance  to  be  practically  pure  lead 
monoxide  (PbO).  It  must  contain  less  than  o.i  per  cent,  of 
metallic  lead,  and  to  be  of  such  fineness  that  not  more  than  0.5 
per  cent,  remains  after  washing  with  water  through  a  No.  21 
silk  bolting  cloth  sieve.  It  must  be  of  good  bright  color  and  be 
equal  to  the  standard  sample  in  freedom  from  vitrified  particles 
and  in  other  respects. 

Chrome  Yellow  (Medium  Orange). — i.  The  dry  pigment  must 
be  of  good  bright  color  and  full  strength,  and  must  contain  at 
least  98  per  cent,  by  weight  of  normal  chromate  or  basic  chro- 
mate  of  lead. 

2.  The  pigment  must  be  of  the  best  quality,  finely  ground  in 
absolutely  pure,  well-settled,  and  perfectly  clear  raw  linseed  oil  of 
the  best  quality  only  to  a  medium  stiff  paste,  which  will  break 
up  readily  in  thinning,  and  must  be  free  from  grit,  adulterants, 
and  all  impurities. 

Specifications  for  Spar  Varnish. — i.  To  be  of  the  best  quality 
and  manufacture  and  equal  in  all  respects,  including  body, 
covering  properties,  gloss,  finish,  and  durability,  to  the  standard 
sample  in  the  general  storekeepers'  offices  at  the  various  navy 
yards.  To  be  made  exclusively  from  the  best  grade  of  hard- 
varnish  resins,  pure  linseed  oil,  pure  turpentine,  and  lead- 
manganese  driers,  and  to  be  free  from  all  adulterants  or  other 
foreign  materials. 

2.  The  varnish  must  not  flash  below  105°  F.  (open  tester),  and 
when  flowed  on  glass  must  set  to  touch  in  from  six  to  twelve 
hours  and  dry  hard  in  from  thirty  to  forty-eight  hours  at  a 
temperature  of  70°  F.  To  be  as  clear  as  and  not  darker  than  the 
standard  sample,  and  to  be  equal  to  it  in  all  respects  as  above 
specified. 

Interior  Varnish. — i.  To  be  of  the  best  quality  and  manu- 


94  ANALYSIS    OF    PAINTS  AND   PAINTING    MATERIALS. 

facture  and  equal  in  all  respects,  including  body,  covering 
properties,  gloss,  finish,  and  durability,  to  the  standard  sample 
in  the  general  storekeepers'  offices  at  the  various  navy  yards; 
to  be  made  exclusively  from  the  best  grade  of  hard-varnish  resins, 
pure  linseed  oil,  pure  spirits  of  turpentine,  and  lead-manganese 
driers,  and  to  be  free  from  all  adulterants  or  other  foreign 
materials. 

2.  The  varnish  must  not  flash  below  105°  F.  (open  tester), 
set  to  touch  in  from  six  to  eight  hours  and  dry  hard  within 
twenty-four  hours  in  a  temperature  of  70°  F.  It  must  stand 
rubbing  with  pumice-stone  and  water  in  thirty-six  hours  without 
sweating,  and  must  polish  in  seventy-two  hours  with  rottenstone 
and  water;  to  be  as  clear  as  and  not  darker  than  the  standard 
sample  and  to  be  equal  to  it  in  all  respects,  as  above  specified. 

Japan  Drier. — i.  Japan  drier  must  not  flash  below  105°  F. 
(open  tester) ;  must  be  of  the  best  quality,  light  in  color,  and 
be  made  from  pure  kauri  resin,  pure  linseed  oil,  pure  spirits  of 
turpentine,  and  lead-manganese  driers,  and  be  free  from  adulter- 
ants, foreign  material,  sediment,  and  suspended  matter.  When 
flowed  on  a  glass  plate  and  allowed  to  drain  in  a  vertical  position 
the  material  must  not  come  off  when  touched  lightly  with  the 
finger  after  from  fifteen  to  sixty  minutes,  and  must  dry  elastic 
in  not  less  than  eight  hours  nor  more  than  twenty-four  hours 
at  a  temperature  of  70°  F.,  and  must  not  rub  up  or  powder  under 
friction  by  the  finger  at  the  end  of  this  time.  When  mixed  with 
pure  raw  linseed  oil  (that  will  not  break  under  600°  F.)  in  the 
proportion  of  eight  parts  of  oil  to  one  part  of  drier  the  mixture 
must  remain  clear  for  at  least  two  hours,  and  when  flowed  on  a 
glass  plate  must  not  come  off  when  touched  lightly  with  the 
finger  at  the  end  of  eight  hours  at  a  temperature  of  about  70°  F. 

Raw  Linseed  Oil. — Must  be  absolutely  pure  well-settled 
linseed  oil  of  the  best  quality;  must  be  perfectly  clear  and  not 
show  a  loss  of  over  2  per  cent,  when  heated  to  212°  F.,  or  show 
any  deposit  of  foots  after  being  heated  to  that  temperature. 
The  specific  gravity  must  be  between  0.932  and  0.937  at  60°  F. 

To  be  purchased  by  the  commercial  gallon;  to  be  inspected  by 
weight,  and  the  number  of  gallons  to  be  determined  at  the  rate 
of  7  1/2  pounds  of  oil  to  the  gallon. 

Boiled  Linseed  Oil. — Must  be  absolutely  pure  kettle-boiled  oil 
of  the  best  quality,  and  the  film  left  after  flowing  the  oil  over 


PAINT    SPECIFICATIONS.  95 

glass  and  allowing  it  to  drain  in  a  vertical  position  must  dry  free 
from  tackiness  in  twelve  hours  at  a  temperature  of  70°  F. 

It  must  contain  no  resin.  The  specific  gravity  must  be 
between  o .  934  and  o .  940  at  60°  F. 

To  be  purchased  by  the  commercial  gallon;  to  be  inspected  by 
weight,  and  the  number  of  gallons  to  be  determined  at  the  rate 
of  7  1/2  pounds  of  oil  to  the  gallon. 

Spirits  of  Turpentine. — i.  The  turpentine  must  be  the  prop- 
erly prepared  distillate  of  the  resinous  exudation  of  the  proper 
kinds  of  live  pine  or  live  pitch  pine,  unmixed  with  any  other 
substance;  it  must  be  pure,  sweet,  clear,  and  white,  and  must 
have  characteristic  odor. 

2.  A  single  drop  allowed  to  fall  on  white  paper  must  com- 
pletely evaporate  at  a  temperature  of  70°  F.  without  leaving  a 
stain. 

3.  The  specific  gravity  must  not  be  less  than  0.862  or  greater 
than  0.872  at  a  temperature  of  60°  F. 

4.  When  subjected  to  distillation,  not  less  than  95  per  cent, 
of  the  liquid  should  pass  over  between  the  temperature  of  308° 
F.  and  330°  F.,  and  the  residue  should  show  nothing  but  the 
heavier  ingredients  of  pure  spirits  of  turpentine.     If  at  the  begin- 
ning of  the  operation  it  shows  a  distillation  point  lower  than  305° 
F.,  this  will  constitute  a  cause  for  rejection. 

5.  A  definite  quantity  of  the  turpentine  is  to  be  put  in  an 
open  dish  to  evaporate,  and  the  temperature  of  the  dish  will  be 
maintained  at  212°  F. ;  if  a  residue  greater  than  2  per  cent,  of  the 
quantity   remains   on   the   dish   it  will   constitute   a   cause   for 
rejection. 

6.  Flash  Tests. — An  open  tester  is  to  be  filled  within  1/4  inch 
of  its  rim  with  the  turpentine,  which  may  be  drawn  at  will 
from  any  one  can  of  the  lot  offered  under 'the  proposal.     The 
tester  thus  filled  will  be  floated  on  water  contained  in  a  metal 
receptacle.     The  temperature  of  the  water  will  be  gradually  and 
steadily  raised  from  its  normal  temperature  of  about  60°  F.  by 
applying  a  gas  or  spirit  flame  under  the  receptacle.     The  tem- 
perature of  the  water  is  to  be  increased  at  the  uniform  rate  of  2°  F. 
per  minute.     The  taper  should  consist  of  a  fine  linen  or  cotton 
twine  (which  burns  with  a  steady  flame),  unsaturated  with  any 
substance.     When  lighted  it  is  to  be  used  at  every  increase  of 
i°  temperature,  beginning  at  100°  F.     It  is  to  be  drawn  horizon- 


96  ANALYSIS    OF    PAINTS  AND    PAINTING    MATERIALS. 

tally  over  the  surface  of  the  turpentine  and  on  a  level  with  the 
rim  of  the  tester.  The  temperature  will  be  determined  by  plac- 
ing a  thermometer  in  the  turpentine  contained  in  the  tester  so 
that  the  bulb  will  be  wholly  immersed  in  the  liquid.  The 
turpentine  must  not  flash  below  105°  F. 

7.  Sulphuric  Acid  Test. — Into  a  30  cubic  centimeter  tube, 
graduated  to  tenths,  put  6  cubic  centimeters  of  the  spirits  of 
turpentine  to  be  examined.  Hold  the  tube  under  the  spigot  and 
then  slowly  fill  it  nearly  to  the  top  of  the  graduation  with  con- 
centrated oil  of  vitriol.  Allow  the  whole  mass  to  become  cool 
and  then  cork  the  tube  and  mix  by  shaking  the  tube  well,  cooling 
with  water  during  the  operation  if  necessary.  Set  the  tube  ver- 
tical and  allow  it  to  stand  at  the  ordinary  temperature  of  the 
room  and  not  less  than  half  an  hour.  The  amount  of  clear  layer 
above  the  mass  shows  whether  the  material  passes  test  or  not. 
If  more  than  6  per  cent,  of  the  material  remains  undissolved 
in  the  acid  this  will  constitute  a  cause  for  rejection. 


INDEX. 


Acetic  acid,  in  white  lead,  4 
Thompson's  method,  4 
navy  method,  5 

Acid  number,  linseed  oil,  52 

Aluminium,       determination      i  n 

mixed  pigments,  41 
separation  from  iron,  41-34 
separation  from  chromium,  3  7 

American    vermilion,   analysis   of, 

35 
Antwerp  blue,  analysis  of,  33 

commercial  method,  34 
Asbestine,  analysis  of,  23 
Asphaltene,  determination  of,  79-86 
Asphaltic  compounds,  distinction 
from  coal-tar  compounds, 

87 

paints,  analysis  of,  78 
Asphaltum  varnish,  specincations, 
army,  91 

B 

Barium  sulphate,  determination  of, 

2  I 

in  barytes,  2 1 

in  blanc  fixe,  2 1 

in  lithopone,  20 

in  mixed  paints,  41,  44,  46 
Barytes,  analysis  of,  21 
Basic  carbonate  white  lead,  anal- 
ysis of,  3 

sulphate  white  lead,    analysis 

of,  17 

Benzine,  analysis  of,  64 
Bituminous  paints,  analysis  of,  78 
Black  pigments,  analysis  of,  38 
Blanc  fixe,  analysis  of,  2 1 
Blue  pigments,  analysis  of,  32 


Calcium,  determination  of,  22 
as  oxalate,  22 
volumetric  method,  23 
carbonate,  analysis  of,  22 
sulphate,  analysis  of,  22 
Thompson's  method,  45 

Carbon  dioxide,  determination  of, 

4 

De  Horvath  method,  1 5 
Scheibler's  method,  6 
China  clay,  analysis  of,  23 
Chinese  blue,  analysis  of,  33 
commercial  method,  34 
specifications,  navy,    92 
wood  oil,  examination  of,  61 
Chromium,  determination  of,3 5,  3 7 
as  oxide,  35 

separation  from  aluminum,  3  7 
separation  from  iron,  37 
Chromes,  specifications,  army,  90 
Chrome  green,  analysis  of,  36 
specifications,  army,  36 
yellow,  analysis  of,  3  5 
specifications,  navy,  92,  93 
Coal-tar     compounds,    distinction 
from  asphaltic  compounds, 
87 


Damar      varnish,       specifications, 

army,  91 

Dietrich  Tables,  9 
Driers,  japan,  analysis  of,  65 
Drop  black,  analysis  of,  3  8 
specifications,  army,  90 


Eschka's  method,  sulphur,  80 


97 


IDNEX. 


Ferrocyanide  solution,  standard  for 

volumetric  zinc,  2 
Flash-point,  linseed  oil,  50 
Foots,  linseed  oil,  50 


Graphite,  analysis  of,  38 
Green  pigments,  analysis  of,  36 
Gypsum,  analysis  of,  22 

H 

Hexabromide  test,  linseed  oil,  53 
Hughes'    method,   sublimed  white 
lead,  17 


Indian  red,  analysis  of,  26 

specifications,  army,  89 
Interior     varnish,     specifications, 

navy,  93 
Iodine  values,  linseed  oil,  52 

mixed  oils,  60 

Iron,  determination  of,  27,  41 
as  oxide,  41 
in  mixed  paints,  4 1 
in  oxides,  27 
separation     from     aluminum, 

4i,  34 

from  chromium,  37 
volumetric,        bichromate 

method,  25 
permanganate  method,  27 

J 
Japan,  analysis  of,  65 

Mcllhiney's  method,  67 
driers,  analysis  of,  65 
specifications,  army,  90 

L 

Lamp-black,  analysis  of,  38 
specifications,  army,  90 

Lead,  as  chromate,  4 
as  sulphate,  3 
volumetric  method,  6 
in  mixed  paints,  41,  43,  44,  47 
impurities  in  metallic  lead,  16 


Lead  chromate,  analysis  of,  35 
dioxide,    determination,    volu- 
metric method,  28 
sulphite,      determination, 

Thompson's  method,  47 
Leaded  zinc,  analysis  of,  18 
Lemon  chrome,  analysis  of,  35 
Light  petroleum  oils,  analysis  of, 

64 
Linseed  oil,  analysis  of,  49 

boiled,     specifications,     navy, 

94 

flash-point,  50 
foots,  50 
iodine  values,  52 
raw,  specifications,  navy,  94 


M 


Magnesium,  determination  as  pyro- 

phosphate,  24 
Mannhardt's     method,     ochers, 

siennas,  umbers,  25 
Maumene  test,   55 
Mcllhiney's  method,  for  Japan,  67 
for  shellac,  7 1 
for  varnish,  67 

Mercury,  gravimetric  methods,  30 
Metallic  brown,  analysis  of,  2  6 

specifications,  navy,  92 
Mineral  black,  analysis  of,  38 
Mixed  paints  and  pigments,  analy- 
sis of,  40 

Thompson's  methods,  43 
Mixed     colored     paints    and    pig- 
ments, analysis  of,  47 


Navy  specifications,  92 
O 

Ocher,  analysis  of,  2  5 

specifications,  army,  90 

Oil       lamp-black,      specifications, 
army,  90 

Orange  chrome,  analysis  of,  35 
mineral,  analysis  of,  28 
pigments,  analysis  of,  35 


INDEX. 


99 


Organic  colors  in  pigments,  exam- 
ination of ,  3 1 


Paint  vehicle,  analysis  of,  48 

separation  from  pigment,  40,  48 
Paris  white,  analysis  of,  22 
Petrolene,  determination  of,  78 
Petroleum  oils,  analysis  of,  64 
Prussian  blue,  analysis  of,  33 
commercial  method,  33 


Red  lead,  analysis  of,  28 
specifications,  navy,  93 
pigments,  analysis  of,  28 
Rosin,  53 

in  linseed  oil,  53,  58 
oil,  determination  of,  53 
Lewkowitsch's  method,  58 
gravimetric  method,  59 
volumetric  method,  58 
as  an  adulterant,  7 1 


Saponification  number,  linseed  oil, 

52 
Separation  vehicle  from  pigment, 

40,   48 
Shellac,  analysis  of,  7 1 

Mcllhiney's  method,  71 
Sienna,  analysis  of,  25 

specifications,  army,  90 
Silex,  analysis  of,  23 
Silica,  analysis  of,  23 

in  mixed  paints,  46 
Sodium,  determination  of,  24 
as  chloride,  2  5 
as  sulphate,  25 

separation  from  potassium,  2  5 
Soluble  sulphates,  in  barytes  and 

blanc  fixe,  22 
Solvent,  for  extraction  of  vehicle 

from  pigment,  40 
Soya  bean  oil,  examination  of,  59 
Spar  varnish,  specifications,  navy, 
93 


Specifications,  army,  89 

navy,  92 
Spirits  of  turpentine,  analysis  of, 

62 

specifications,  navy,  95 
Sublimed    white    lead,     complete 

analysis,  17 
Sulphates,   in  barytes   and   blanc 

fixe,  22 

in  sublimed  white  lead,  1 7 
Sulphur,  Eschka's  method,  in  as- 
phaltic     and     bituminous 
compounds,  80 
in  ultramarine  blue,  33 
Sulphur  dioxide,  in  sublimed  white 
lead,  1 8 


Turpentine,  spirits  of,  analysis  of, 

6-1 
specifications,  navy,  95 


Ultramarine    blue,    average   com 
position,  33 


Varnish,  analysis  of,  65 

damar,    specifications,     army, 
9i 

interior,    specifications,    navy, 
93 

Mcllhiney's  method,  67 

spar,  specifications,  navy,  93 

specifications,  army,  91 
Vehicle,  analysis  of,  48 

separation  from  pigment,  40, 48 
Venetian  red,  analysis  of,  26 

specifications,  army,  89 
Vermilion,  analysis  of,  29 

specifications,  army,  90 
Viscosity,  linseed  oil,  49 

W 

Water,  in  vehicle,  Nemzek  method, 
48 


100  INDEX. 

White  lead,  analysis  of,    3  Zinc,  as  oxide,  i 

specifications,  army,  89  volumetric  method,  i 

navy,  92  in  mixed  paints,  42 

White  pigments,  analysis  of,  i  Zinc  chromate,  analysis  of,  3  5 

Whiting,  analysis  of,  2  2  lead,  analysis  of,  1 8 

specifications,  navy,  92  oxide,  analysis  of,  i 

specifications,  army,  89 
sulphide,  in  lithopone,  20 
Zinc,  determination  of,  r 


14  DAY  USE 

RETURN  TO  DESK  FROM  WHICH  BORROWED 

LOAN  DEPT. 

This  book  is  due  on  the  last  date  stamped  below,  or 

on  the  date  to  which  renewed. 
Renewed  books  are  subject  to  immediate  recall. 


General  Library 

University  of  California 

Berkeley 


LD  21A-50m-4,'59 
(A1724slO)476B 


U,C.  BERKELEY  LIBRARIES 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


